A substrate for a recording head includes a circuit through which current flows upon impression of a source voltage, irrespective of the operating state of an energy converting element, and a current cutoff means for cutting off current to the circuit in response to an entered control signal. A reset signal for achieving a standby state of the printing operation serves as the control signal. The current cutoff circuit is operated when the reset signal is active in an H state, and it cuts off the constant current. By cutting off the constant current, the leak current of a heater power source VH may be accurately measured, permitting determination of whether the source voltage wiring is properly insulated from other circuit elements of the substrate. The constant current may also be cut off in the standby state, in which printing is not performed, so as to reduce power consumption.