A signal transmission device 100 includes an isolated signal transmission circuit 10 configured to transmit a pulse signal from a primary circuit system 1p via a first isolating element ISO1 to a secondary circuit system 1s, and an isolated power supply control circuit 20 which serves as a controlling agent of an isolation-type power supply that generates a second supply voltage Vcc2 for the secondary circuit system 1s from a first supply voltage Vcc1 for the primary circuit system 1p and which transmits an output feedback signal of the isolation-type power supply from the secondary circuit system 1s via a second isolating element ISO2 to the primary circuit system 1p.