A foldable storage box, comprising: a rectangular base board; an opposing board opposing said base board; a pair of side wall boards connected between a side edge of said base board and a side edge of said opposing board, said pair of side wall boards in a folded state allowing said base board and said opposing board to move closer and becoming an open state from the folded state when said opposing board is moved away from said base board, said pair of side wall boards surrounding four sides together with said base board and said opposing board in the open state; a bottom board disposed in a stored state to be overlaid with said base board and said opposing board when in the folded state of said side wall boards, and axially supported to rotate freely on said base board or said opposing board, said bottom board transitioning from the stored state to the open state by moving rotatably to form a bottom part surrounded on four sides by said pair of side wall boards, said base board, and said opposing board, when said opposing board is moved away from said base board and said side wall boards are transitioned from the folded state to the open state; and a lock unit for locking said side wall boards in the open state when said bottom board and the side wall boards are transitioned from the stored state to the open state, said storage box being characterized in that said lock unit comprises: a pressing part disposed on a side surface of said bottom board to be rotated and placed projecting toward the side wall board; and a lock device provided on said side wall boards, said lock device having a rotating member to be pressed to rotate by said pressing part while said bottom board is rotated from the stored state to the open state, to lock said side wall boards in the open state or while said botton board is rotated back from the open state to the stored state, to unlock the lock. a rectangular base board; an opposing board opposing said base board; a pair of side wall boards connected between a side edge of said base board and a side edge of said opposing board, said pair of side wall boards in a folded state allowing said base board and said opposing board to move closer and becoming an open state from the folded state when said opposing board is moved away from said base board, said pair of side wall boards surrounding four sides together with said base board and said opposing board in the open state; a bottom board disposed in a stored state to be overlaid with said base board and said opposing board when in the folded state of said side wall boards, and axially supported to rotate freely on said base board or said opposing board, said bottom board transitioning from the stored state to the open state by moving rotatably to form a bottom part surrounded on four sides by said pair of side wall boards, said base board, and said opposing board, when said opposing board is moved away from said base board and said side wall boards are transitioned from the folded state to the open state; and a lock unit for locking said side wall boards in the open state when said bottom board and the side wall boards are transitioned from the stored state to the open state, said storage box being characterized in that said lock unit comprises: a pressing part disposed on a side surface of said bottom board to be rotated and placed projecting toward the side wall board; and a lock device provided on said side wall boards, said lock device having a rotating member to be pressed to rotate by said pressing part while said bottom board is rotated from the stored state to the open state, to lock said side wall boards in the open state or while said botton board is rotated back from the open state to the stored state, to unlock the lock. a pressing part disposed on a side surface of said bottom board to be rotated and placed projecting toward the side wall board; and a lock device provided on said side wall boards, said lock device having a rotating member to be pressed to rotate by said pressing part while said bottom board is rotated from the stored state to the open state, to lock said side wall boards in the open state or while said botton board is rotated back from the open state to the stored state, to unlock the lock.