Volume change compensation device and damper device

A volume change compensation device connected to a hydraulic fluid housing portion liquid-tightly housing hydraulic fluid including liquid to compensate for a change in a volume of the hydraulic fluid, comprising:

• a body tube formed in a tubular shape, communicating with the hydraulic fluid housing portion at one opening, and housing part of the hydraulic fluid;
• an inner cylinder piston formed in a bottomed cylindrical shape and slidably provided along an axis direction in a state in which the part of the hydraulic fluid is housed in the body tube;
• an inner cylinder inner small piston slidably provided along the axis direction in the inner cylinder piston;
• and
• an inner cylinder piston pressing elastic body provided on an opposite side of the inner cylinder piston from a side of the one opening in the body tube and elastically pressing the inner cylinder piston toward the one opening side,
• wherein the inner cylinder piston is, in the body tube, arranged in such an orientation that the inner cylinder piston opens to the one opening side, and an air hole for an air flow into the inner cylinder piston is formed at a bottom portion of the inner cylinder piston facing the inner cylinder inner small piston.