To provide a passenger detecting system which not only can accurately detect the seating conditions of passengers, but also can appropriately control an air bag device, etc., based on the detected results.

A crew detecting system is provided with an electric field generating means 11 which generates an electric field around a plurality of antenna electrodes arranged on a sheet, a switching circuit 18 which selectively switches and connects the generating means 11 to a specific one of the antenna electrodes, an information detecting circuit 15 which generates an electric field around the specific antenna electrode selected by means of the switching circuit 18 and detects the information related to the current flowing to the antenna electrode based on the electric field, and a control circuit 22 which fetches the signal outputted from the detecting circuit 15 and discriminates the seating conditions, etc., of passengers based on the data of the signal. The electric field generating means 11 is constituted to output a high-frequency low voltage having a nearly square waveform.