To enhance measuring precision for an occupant weight by precluding a horizontal-directional load from being transmitted to a load sensor.

This occupant weight measuring instrument 1 is provided with fixed lower rails 3 fixed onto a floor of a cabin, movable upper rails 4 engaged with the fixed lower rails 3 to be slidable along a longitudinal direction with respect to the fixed lower rails 3, the load sensors 70, 80 provided to be slide-movable laterally with respect to the movable upper rails 4, and a sub-frame 110 mounted on the load sensors 70, 80. Laterally long slots 75, 85 are formed in flanges 71, 81 of the load sensors 70, 80, stepped screws 77, 87 are inserted into the slots 75, 85, and the stepped screws 77, 87 are screwed in to upper faces of the movable upper rails 4. The stepped screws 77, 87 are inserted into the the slots 75, 85 to be freely slidable over longitudinal directions of the slots 75, 85.