PURPOSE: To make it possible to add a monitor function by slight addition to an existing facility even if a multistory parking space is not provided with a function to monitor car weight and eliminate the need for a new installation of a multi-story parking space or a large-scale work and thereby minimize cost required for the addition of the monitor function.

CONSTITUTION: A common lift space, which extends in the vertical direction, and a plurality of parking spaces, which are located on both sides of the space, are installed inside a multi-story parking space. A lift 6 is installed to the lift space where a transverse tray is installed to a parking space. The lower end of the lift space is used as a car entrance and exit 4 where a stop floor 15, which receives a halted car is laid out together with the lift 6. A plurality of forks 21a, 21b, 21c and 21d are mounted at a contact spot with front wheels 11 of a car on the stop floor 15. A controller 26 detects an amount of strain based on a signal transmitted from each strain gauge 24 and determines the weight of car equivalent to the amount of strain, thereby displaying the value on a weight indicator 25.