To automatically perform correction, when an output level is fluctuated by always monitoring the output level of a signal by feeding back the outputted signal and comparing its level with an initially set level through a level comparator part.

The signal, oscillated from a signal oscillating part 3, is controlled corresponding to the initially set level by a level control part 4 and outputted from a signal output part 5. Moreover, a level comparator part 7 is provided inside a signal output device 1, the level of a feedback signal, feeding back the signal outputted from the signal output part 5 is compared with the initially set level from a control part 8 and when any error is generated in the level, the signal is outputted again after its output level is corrected. Therefore, the malfunction of a receiver caused by the fluctuation of level is prevented, and even when the phenomenon of such a malfunction is generated, by monitoring the fluctuation range of level, it is effective for specifying the factor of malfunction.