Neutral position locking apparatus and rear wheel steering system including the same

A neutral position locking apparatus that restricts a movement in a rack axis direction, of a rack shaft that steers rear wheels, the neutral position locking apparatus comprising:

• a restriction pin having a first pin-sidewall portion that restricts the movement of the rack shaft in the rack axis direction at a neutral position, and a second pin-sidewall portion that restricts the movement of the rack shaft in the rack axis direction at a restriction position that is different from the neutral position;
• a pin-receiving portion formed in the rack shaft and having a first shaft-sidewall portion that restricts the movement of the rack shaft in the rack axis direction by making contact with the first pin-sidewall portion when the rack shaft is located at the neutral position, and a second shaft-sidewall portion that restricts the movement of the rack shaft by making contact with the second pin-sidewall portion when the rack shaft is located at the restriction position;
• and
• a driving device that moves the restriction pin in a projection direction in which the restriction pin moves toward the pin-receiving portion and in a removal direction in which the projection pin moves away from the pin-receiving portion, wherein:
• the restriction pin and the pin-receiving portion are configured such that a force in the removal direction, which the second pin-sidewall portion receives from the second shaft-sidewall portion, is zero, or configured such that a force in the removal direction, which the second pin-sidewall portion receives from the second shaft-sidewall portion, is smaller than a force in the removal direction, which the first pin-sidewall portion receives from the first shaft-sidewall portion.