A method for checking an error control unit in a circuit, wherein the error control unit generates an error signal, when operating properly, if the digital circuit is in an error state. The method includes the following steps: invoking the state indicating the error, monitoring the error signal, and generating an alarm signal when the error signal does not appear or appears incorrectly. A device for checking an error control unit of a circuit, wherein the error control unit generates an error signal when it is operating properly if the circuit is in or outputs a state indicating an error, has a device for inducing the state indicating the error, and a device for monitoring the error signal and generating an alarm signal when the error signal does not appear or appears incorrectly after the state indicating the error was induced.

For making outputs of a drive circuits accurate, the drive circuit is composed of a plurality of current signal generation circuits for outputting a current signal to each of a plurality of output units, a current signal output line to which outputs of the plurality of current signal generation circuits are commonly connected, a correction value output circuit for outputting a correction value obtained by evaluating the output of one or more specific circuits of the plurality of current signal generation circuits on a basis of current values output through the current signal output line, and a correction circuit for correcting an image signal supplied to the current signal generation circuits by means of the correction value.