A movable part which combines with a stationary part to form a bed includes: a contact sensor (50); wheels (44) rotatable in all directions; a body drive unit (31) which drives the wheels (44); an avoidance instruction unit (51) which generates an avoidance instruction according to a result of detection by a contact sensor (50); a rotation center setting unit (52) which sets a rotation center Q2 for the avoidance instruction; an avoidance instruction translation unit (54) which translates the avoidance instruction and the rotation center Q2 into a move instruction; and a position detection unit (34) which detects a positional relationship to a docking area (20), and the rotation center setting unit (52) sets the rotation center according to the positional relationship detected by the position detection unit (34).