Distance measurements are performed by a fork pocket detection sensor at a position at which the fork pocket detection sensor faces one of fork pockets and at a position at which the fork pocket detection sensor faces the central position in the horizontal direction between the fork pockets on a pallet side face, and information obtained by combining pieces of distance-measurement information acquired by the distance measurements is compared with information of predefined shapes of the fork pockets, so as to specify the positions of the fork pockets. Hereby, it is possible to accurately detect the positions of the fork pockets without causing a decrease of conveyance efficiency.