The present invention can provide a pressure sensor provided with a relay substrate that can be connected to the pressure sensor and convert the drive voltage or the pressure detection signal, a relaysubstrate therefor, and a relay substrate unit therefor in order to cope with various drive voltages or various signal types of pressure detection signals. The pressure sensor according to the present invention is featured by including: a pressure sensor unit provided with a pressure detecting element configured to receive a drive voltage from a control substrate and electrically send a pressuredetection signal to the control substrate so as to detect a pressure of fluid, and a plurality of electric wires connected to the pressure detecting element so as to supply the drive voltage and drawnto the outside so as to send the pressure detection signal; and a relay substrate connected to the plurality of electric wires and having a converting circuit mounted thereon, the converting circuitconverting either or both of the drive voltage supplied from the control substrate and the pressure detection signal sent to the control substrate.