Electronic circuit unit and battery pack

An electronic circuit unit includes a trigger circuit and a circuit module. The trigger circuit includes a semiconductor switching element configured to output a switching pulse signal in response to an external trigger signal, a load resistor for the semiconductor switching element, a one-shot pulse circuit configured to convert the switching pulse signal into a one-shot pulse with a predetermined pulse width, and a forcible-reset circuit connected to an input side of the semiconductor switching element. The one-shot pulse circuit includes a coupling capacitor connected to an input side of the semiconductor switching element and a charging resistor for the coupling capacitor. The pulse width of the one-shot pulse is determined by a time constant of the coupling capacitor and the charging resistor. The forcible-reset circuit is configured to temporarily input an on-voltage to the semiconductor switching element so as to forcibly switch the circuit module to the operating mode.