PURPOSE: To check whether the light emitting element of a preparatory electro- optical conversion part is normal without taking labor in a light transmission terminal office apparatus having an actually used electro-optical conversion part and the preparatory electro-optical conversion part set to a cold standby state.

CONSTITUTION: A noneffective means 12 not exerting effect on reception on a receiving side even when a preparatory electro-optical conversion part 11 is started and a nomality and abnormality detection part 13 controlling the noneffective means 12, starting the preparatory electro-optical conversion part 11 and confirming whether and alarm is outputted from a output monitor part 4 to judge whether a light emitting elament 2 is normal are provided.