The present invention aims at providing a battery pack monitoring circuit capable of detecting an open circuit in a part connecting an electrode terminal of a battery pack and a power supply terminal of a battery voltage monitoring circuit. The battery voltage monitoring circuit includes: a first power supply terminal (VDD) to be connected to the positive terminal of the battery pack; a first supply voltage sensing terminal (V5) to be connected to the positive terminal of the battery pack; a first resistor (R03) connected between the first power supply terminal (VDD) and the first supply voltage sensing terminal (V5); a second resistor (R00) connected between a second supply voltage sensing terminal (V4) and the first power supply terminal (VDD), wherein the second supply voltage sensing terminal (V4) is connected to a negative terminal of a positive terminal side rechargeable cell (B5) which is connected to the positive terminal of the battery pack; and a first comparator (COM2) configured to compare a voltage at the first power supply terminal (VDD) and a voltage at the first supply voltage sensing terminal (V5).