A key sheet module comprising a single-sided printed wiring board including a front surface on which a plurality of wiring patterns are provided and a plurality of holes provided at predetermined positions, rear-surface connection parts for the wiring patterns being exposed from the holes on a rear surface of the single-sided printed wiring board, an insulating layer provided on the front surfaceof the single-sided printed wiring board and having openings, patterns for switching of the wiring patterns and front-surface connection parts of the wiring patterns being exposed in the openings, the front-surface connection parts being connected by a front-surface jumper and the rear-surface connection parts being connected by a rear-surface jumper, respectively.