PURPOSE: To lessen a load of a signal processing part and to save electric power consumption as well by inputting the minimum required wave shape signal only, corresponding to using purpose and using conditions.

CONSTITUTION: A signal processing circuit 2 analyzes input wave shape signal with referring to necessary data, and judges whether the wave shape signal is the wave shape to be detected or not. A pre-processing part 3 has a function to limit the wave signal to be input into the signal processing circuit 2 from all the input wave signals. For example, the part 3 is provided with a filter with which only a certain frequency band can pass through, a limiter which cuts off level higher than a certain level, a cripper with which signal higher than a certain level only can pass through, and so on. Furthermore, the pre- processing part 3 is provided with a level changing circuit to set forth a signal input level to the signal processing circuit 2.