It is provided a subsystem for seat weight detection, the configuration of which enables improved assemblability and economization of space in layout. A seat weight detecting subsystem is provided for each seat 7 mounted inside a vehicle. Each seat weight detecting subsystem 4 includes weight detection sensors 8 which are installed in a seat 7, and a power supplying member 9 which is connected to the weight detecting sensors 8, a power supply 5, an ECU 3 and the like. The power supplying member 9 is provided with an FPC 10 and a seat side ECU functional portion 11 that is integratedly attached to the FPC 10. The seat-side ECU functional portion 11 includes sensor connecting sections 13, a signal receiving section 14, a data generating section 15, and a data outputting section 16.