To provide an apparatus for detecting a crew member, which apparatus can detect the disconnection between a control device and a load sensor without increasing the impedance of the signal system line.

A load sensor 14 acquires the load information corresponding to the load applied to a seat body. An electric control unit (ECU) 20 is connected to the load sensor 14 via a signal line 21, etc., so as to carry out a digital bidirectional communication. The ECU 20 carries out the judgment of the existence of the crew member by receiving the load information signal corresponding to the load information sent from the load sensor through sending an information requiring signal to the load sensor 14. First power source wiring L1, etc. has an H (high) level potential, and supplies an electric current to the ECU 20 and the load sensor 14. Second power source wiring L2, etc. has an L (low) level potential, and supplies an electric current to the ECU 20 and the load sensor 14. The ECU 20 comprises a transistor 24, and a pull-up resistor 23 connected to the first power source wiring L1 at its one end and connected to signal wiring L3 at the other end. The load sensor 14 comprises a field effect transistor (FET) 33.