The invention provides a shaft slip-off stopping structure which has sufficient strength and is difficult to pull out, and the structure is formed by minimum number of necessary components. The shaft slip-off stopping structure comprises a shaft inserted member (3) into which a shaft is inserted in a relatively movable manner, and a locking mechanism (43) provided in the shaft inserted member. The tip portion of the shaft includes a locking step portion formed by providing an annular groove or a ring-shaped projection portion. The locking mechanism (43) includes at least two locking pieces arranged around the shaft at an equal interval. The shaft is stopped from slipping off by a tip portion of each of the tip locking portions abutting on the locking step portion. The locking piece can receive the force in a pulling direction in a length direction of the locking piece, whereby a load can be reduced. That is, sufficient strength can be maintained.