A discharge control apparatus arranged in a power conversion system having high-side switching element and low-side switching element to convert the DC power from the battery to a predetermined type of power. The discharge control is performed to discharge a capacitor connected in parallel to the switching elements when an abnormal event occurs. The discharge control apparatus is configured to simulate the operation of the switching elements assuming occurrence of the abnormal event, and transmits a plurality of signals representing the simulation result to a control device via a common photocoupler that isolates the switching elements side and the control device side. The control device diagnoses whether or not a fault occurs in the discharge control or the like by the simulation result.