The member joining device includes: a tubular unit including a tubular assembly that is fixed, a flange portion whose position in a first central axis direction is fixed with respect to the tubular assembly; a shaft unit that includes a shaft assembly inserted into the tubular assembly in a linearly movable manner, and a protrusion portion whose position in a second central axis direction is fixed with respect to the shaft assembly, wherein the protrusion portion is positioned radially outside the first central axis of the tubular assembly, the protrusion portion faces the flange portion in the central axis direction; a rubber member arranged radially outside the tubular assembly, between the protrusion portion and the flange portion in the central axis direction; and a motion mechanism that moves the shaft unit in the central axis direction with respect to the tubular unit.