An overcurrent protection device satisfactorily detects overcurrent without adding complicated component or occupying large space. Penetration member penetrates board face A having a first wiring circuit and face B with a second one, transmitting heat from face A to B. Connection/disconnection part is inserted into first wiring circuit, switching current to heat generation part for generating heat with current, formed in portion of first circuit, continued with one end of penetration member. Temperature detection member disposed near or abutted against other end of penetration member on face B detects transmitted heat, outputting signal. Control part controls connection/disconnection part on signal. Heat generation part is narrower than width w1 not generating heat in steady state, having width w2 to raise temperature upon overcurrent, and being sandwiched between patterns with width w1. Control part turns off current with heat generation part temperature raised to or above prescribed threshold.