Patent ID: 8002374

Claim:
A printhead substrate having a plurality of first heating elements comprising: a power supply line, connected to each of the plurality of first heating elements, for supplying a predetermined voltage; a plurality of first wiring lines, each having a first wiring resistance, connected to the power supply line, and each of the plurality of first wiring lines being connected to one end of one of the plurality of first heating elements; a plurality of first switching elements, each being connected to the other end of one of the plurality of first heating elements and controlling the one of the plurality of first heating elements; a second wiring line, having a second wiring resistance, connected to the power supply line and one end of a second heating element; a second switching element, connected to the other end of the second heating element, for controlling the second heating element; a reference power supply which sets a reference voltage; a comparison circuit which compares the reference voltage with a voltage based on the second wiring resistance and outputs a first signal based on the comparison; and a control circuit which inputs the first signal and outputs a second signal for controlling driving of each of the plurality of first switching elements, based on the first signal, wherein the plurality of first wiring lines and the second wiring line are formed in a same manufacturing step so that the first wiring resistance and the second wiring resistance exhibit a same characteristic.