A power source circuit shut off apparatus shuts off a circuit of a battery assembly in which plural battery cells connected in series are arranged in parallel. The power source circuit shut off apparatus includes a housing, a pair of bus bars that is arranged in the housing and is connected to the adjacent battery cells respectively, a switch section that is adapted to conduct electrical connection or disconnection between the pair of bus bars, and a retaining member which is formed on the housing and is configured to be retained to a resin frame part of a side surface of the battery cell.