PURPOSE: To attain high speed response to a light emitting element by interposing a delay element to one branch of a current changeover switch.
CONSTITUTION: A current flowing to one current branch 12 of a current changeover switch 2 in response to an input data pulse is retarded by a delay element 4 and the sum of the retarded current and a current flowing to other current path 6 of the current changeover switch 2 flows to a light emitting element 8. Since the drive of large amplitude is caused at the leading and trailing of the current sum, the response of light emission and extinction of the light emitting element is improved. Since the amount of delay element in a current increment generating system to cause the characteristic depends on the improvement of the response and is not dependent on the bit rate of an input data pulse. Moreover, the current increment generating system is independent of the normal drive current application system and of the drive waveform.