Adapter

1. An adapter comprising: a male member; an arm that faces the male member; and a claw that is provided on the arm so as to protrude toward the male member,

wherein the adapter is configured to be connected to a female connector with the male member being inserted into the female connector and the claw engaging with the female connector,

the arm is elastically deformable so that the claw can move away from the male member,

the claw includes a slidable portion that slides on the female connector during a process in which the adapter is connected to the female connector,

the slidable portion is configured to move the claw away from the male member while the slidable portion slides on the female connector,

a contour shape of the slidable portion seen in a direction that is orthogonal to a central axis that passes through the male member includes a smooth convex curve, and

the slidable portion is provided on a rib that is a thin plate that extends along a plane that includes the central axis, or along a plane that is parallel with a plane that includes the central axis.

2. The adapter according to claim 1 , wherein the smooth convex curve is an arc or a portion of an ellipse.

3. The adapter according to claim 1 , wherein the male member is a puncture needle that has a sharp leading end.

4. The adapter according to claim 1 ,

wherein the female connector includes a plug member of a vial bottle, and

the claw engages with a flange that has an expanded diameter and surrounds the mouth of the vial bottle.