The amount of processing liquid consumed from the processing liquid in the tank is calculated based on the history of opening and closing events of one or more of the valves, and that the anomaly detection controller of the substrate processing apparatus generates a level sensor failure alarm if the calculated amount of consumed processing liquid has increased beyond a state transition liquid consumption amount and yet the level sensor has not switched from the first state to the second state. The substrate processing apparatus and the level sensor are designed so that the level sensor switches from the first state to the second state when the calculated amount of consumed processing liquid has increased beyond the state transition liquid consumption amount.