Seating sensor system, failure state detecting method using seating sensor and industrial vehicle with seating sensor system

A seating sensor (11) detects whether a seat (2) is occupied by a person. A microcomputer (12) determines whether the seat (2) is occupied by a person based on the output of the seating sensor (11). If a seating signal indicating that the seat (2) is occupied by a person is supplied continuously for over a predetermined time, the microcomputer (12) outputs an alarm signal indicating that the seating sensor system is in a failure state.