To securely stack packs moving on a conveyance line in predetermined number of steps at high speed and simplify a configuration.

This pack step stacking mechanism is composed of a mechanism main body 6 elevating and lowering at a predetermined position on a conveyance conveyor C, a pair of hoisting arms 2, 2 attached to the mechanism main body openably and closably through a hinge 2a, a driven roller 3 attached to the halfway on their inner sides through a hinge 3a, and a cam plate 4 which is positioned between driven rollers 3 on both sides rolling along it and constitutes guide lines 4a on both sides at an upper part initial position 4a1 and in an advance part 4a2 protruding outward just below it, a straight part 4a3 below it, and a lower part retraction part 4a4 just below it. When each driven roller 3 elevates and lowers along the guide line 4a of the cam plate 4 in accordance with elevation and lowering of each hoisting arm 2, both hoisting arms 2 lock the pack S and hoist it by a locking hook 2b at a lower end when elevating and open to drop it when lowering.