An abnormality determination apparatus is applied to a battery pack including blocks composed of battery cells connected in series, and a connecting member that connect blocks to one another in series. In the blocks and the connecting member, a first detection circuit detects a voltage of a first series circuit including the connecting member. A closed-circuit forming unit forms a closed circuit so as to allow a current to flow to the connecting member. The closed circuit includes the connecting member, at least one of the battery cells, and a diode connected in parallel to the connecting member. When a charge-discharge current is not flowing to the battery pack, a first abnormality determining unit determines whether or not an open abnormality has occurred in the connecting member, based on a detection value from the first detection circuit in a state in which the closed-circuit forming unit is forming the closed circuit.