Crane

1. A crane comprising:

a raising member including a distal end and a proximal end, and extending in a longitudinal direction;

a supporting body that supports the raising member to be raised and lowered; and

a raising device that includes a guylink having a first end and a second end, the first end being connected to the distal end of the raising member, the second end being located in an opposite side of the first end, and a pull unit connected to the second end of the guylink to pull the guylink, the raising device being configured to adjust a force with which the guylink pulls the raising member and thus raising the raising member;

a lift rope hung from the distal end of the raising member to lift a cargo;

a lift winch that winds up and winds out the lift rope;

a mid-support rope that connects a middle portion of the raising member to the guylink and includes a securing end secured to the guylink at a point between the first end and the second end of the guylink, and a held portion extending from the securing end toward the raising member;

a constraining unit that is disposed on a middle portion of the raising member to constrain the held portion of the mid-support rope; and

a mid-support winch that winds up and winds out the held portion of the mid-support rope to change a distance between the guylink and the constraining unit.

2. The crane according to claim 1 , further comprising:

a characteristic value detector that detects a characteristic value of the raising member or the mid-support rope, the characteristic value changing with a change in a warp degree of the raising member that warps along a longitudinal direction by a weight of the raising member or a load of the cargo;

circuitry configured to store in advance a relationship between the warp degree of the raising member and the characteristic value and configured to output a warp degree of the raising member, the warp degree corresponding to the characteristic value detected by the characteristic value detector; and

a display that displays the warp degree of the raising member of said output.

3. The crane according to claim 2 , wherein

the characteristic value detector includes a tensional force detector that detects a tensional force of the mid-support rope as the characteristic value.

4. The crane according to claim 2 , further comprising:

a manipulation controller that receives an instruction for manipulating the raising device and the mid-support winch; and

a winch controller that controls an operation of the raising device and winding up and winding out performed by the mid-support winch according to the instruction that the manipulation controller receives.

5. The crane according to claim 4 , wherein

the circuitry is configured to store in advance a target value of the characteristic value set so as to approach approximately zero warp degree of the raising member, and

the winch controller has an automatic-control mode in which the mid-support winch is controlled to wind up and wind out the mid-support rope so as the characteristic value detected by the characteristic value detector to approach the target value.

6. The crane according to claim 1 , wherein

the constraining unit is a mid-support sheave disposed on the raising member to oppose the guylink and stretches the mid-support rope, and

the mid-support winch is disposed on the proximal end of the raising member or on the supporting body so as to wind up and wind out the mid-support rope that is stretched by the mid-support sheave to be further pulled and extended downward.