A member joining device, comprising: a tubular unit that includes a tubular assembly that is fixed and has a first central axis, and a first receiving portion and a second receiving portion; a shaft unit that includes a shaft assembly that is inserted into the tubular assembly in a linearly movable manner and has a second central axis that extends in the same direction as the first central axis, and a first pressing portion and a second pressing portion, wherein the first pressing portion and the second pressing portion are positioned radially outside the first central axis of the tubular assembly, the first pressing portion faces the first receiving portion in the first and second central axis (L1, L2) directions, and the second pressing portion faces the second receiving portion in the first and second central axis (L1, L2) directions; a first elastic member arranged radially outside the first central axis of the tubular assembly, between the first pressing portion and the first receiving portion in the first and second central axis (L1, L2) directions; a second elastic member arranged radially outside the first central axis of the tubular assembly, between the second pressing portion and the second receiving portion in the first and second central axis (L1, L2) directions; and a motion mechanism (70, 80) that moves the shaft unit in the first and second central axis (L1, L2) directions with respect to the tubular unit for compressing and expanding the first and second elastic member radially outside; characterized in that positions of the first receiving portion and the second receiving portion in a first central axis direction are fixed with respect to the tubular assembly, and positions of the first pressing portion and the second pressing portion in a second central axis direction are fixed with respect to the shaft assembly. a tubular unit that includes a tubular assembly that is fixed and has a first central axis, and a first receiving portion and a second receiving portion; a shaft unit that includes a shaft assembly that is inserted into the tubular assembly in a linearly movable manner and has a second central axis that extends in the same direction as the first central axis, and a first pressing portion and a second pressing portion, wherein the first pressing portion and the second pressing portion are positioned radially outside the first central axis of the tubular assembly, the first pressing portion faces the first receiving portion in the first and second central axis (L1, L2) directions, and the second pressing portion faces the second receiving portion in the first and second central axis (L1, L2) directions; a first elastic member arranged radially outside the first central axis of the tubular assembly, between the first pressing portion and the first receiving portion in the first and second central axis (L1, L2) directions; a second elastic member arranged radially outside the first central axis of the tubular assembly, between the second pressing portion and the second receiving portion in the first and second central axis (L1, L2) directions; and a motion mechanism (70, 80) that moves the shaft unit in the first and second central axis (L1, L2) directions with respect to the tubular unit for compressing and expanding the first and second elastic member radially outside; positions of the first receiving portion and the second receiving portion in a first central axis direction are fixed with respect to the tubular assembly, and positions of the first pressing portion and the second pressing portion in a second central axis direction are fixed with respect to the shaft assembly.