In an apparatus for preventing runaway of carriers in a power-and-free conveyor, each of the carriers has a runaway preventing stopper rotatable about its center portion in a substantially vertical plane parallel with the direction of advance of the conveyor, and a restraining member engageable with one end of the stopper for usually preventing the other end thereof from turning forward. The stopper is biased always by weighted arm to turn the other end forward. Runaway preventing contact members are arranged at a spacing in each of rising and falling gradient sections of the conveyor along the path of movement of the stopper other end. When the carrier runs out of control in the falling gradient section, the stopper other end collides with one of the contact members and is thereby turned rearward into engagement with the restraining member against the weighted arm while bringing the one end of the stopper into engagement with another contact member to prevent the carrier from running away. In the event of runaway in the rising section, the other end of the stopper comes into engagement with one of the contact members with its one end in engagement with the restraining member to prevent the carrier from running out of control.