A motor-powered opening/closing apparatus includes a circuit (Q1, R1, Q4) for detecting a constrained state of the motor (10) and deenergizing the motor (10), and a circuit (4, Q4) for detecting clamping of a foreign object between an edge of the window (2) or the door and a fixed frame (1) and stopping or reversing rotation of the motor (10). These circuits (Q1, R1,Q4,4) are independently arranged to detect clamping of the foreign object with high sensitivity while a closing force at the closed position can be kept large. The circuit (Q1, R1, Q4) for detecting a constrained state utilises motor current reversal noise to obtain a rapid response.