Abstract: Box forming apparatus for forming a box from a box blank. The blank has a base with first, second, third and fourth side members extending along respective sides of the base. One of the opposed pairs of side members has parallel inner and outer portions. The other pair has flaps extending from each opposed end. In the apparatus, a pair of spaced, parallel frame members are slidably mounted on a fixed framework. A box forming plate moves vertically between the frame members. A rectangular box forming piston moves vertically between the frame members in alignment with and against the box forming plate. The forming plate and piston have the same size and shape as the box blank's base. A movable frame is provided for vertical displacement beneath the frame members. A flap tuck mechanism on the first frame members folds the flaps perpendicular to the other side members. The flap tuck mechanism is actuated by vertical displacement of the movable frame toward the frame members.