This resin vessel is: provided with a body section (4) of which the transverse cross-sectional shape is approximately a square; and provided below the center in the vertical direction of the body section (4) with a cushion section (27) that can elastically deform in the vertical direction and has across the entire perimeter a groove (28) that becomes wider to the outside in the radial direction. An arced section (32) is formed at the corners of the transverse cross-sectional shape of the groove (28).
