Resin container

1. A resin container comprising:

a body portion having an approximately square cross-sectional shape;

a vertically elastically deformable cushion portion provided downwardly of a vertical center of the body portion, the cushion portion having along its entire circumference a V-shaped concave groove which is formed progressively wider radially outwards, the V-shaped concave groove defining a spring structure in the cushion portion that allows elastic deformation of the cushion portion in a vertical direction; and

an arcuate portion provided at a corner portion in a cross-sectional shape of the V-shaped concave groove,

wherein the arcuate portion is provided at each and every one of four corner portions in the cross-sectional shape of the V-shaped concave groove of the cushion portion,

wherein each arcuate portion has a circle center located at the center of the cross section of the body portion including the arcuate portions, and

wherein the cross-sectional shape of the V-shaped concave groove includes at least one pair of straight segments along which the V-shaped concave groove extends on opposing sides of the resin container.

2. The resin container according to claim 1 , wherein all of the four arcuate portions have a same curvature radius and a same arc length.

3. The resin container according to claim 1 , wherein the cushion portion includes a small concave portion along the entire circumference of the body portion, the small concave portion being shallower than the V-shaped concave groove and the small concave portion includes a first small concave portion provided above the V-shaped concave groove and a second small concave portion provided below the V-shaped concave groove.

4. The resin container according to claim 1 , wherein the cross-sectional shape comprises an approximate rectangle.