PURPOSE: To eliminate the necessity of switching operation of an electric power source switch and a reproducing switch by operating a sound signal generating device for the prescribed time only by touching with the signal generating part of a membrane- shaped piezoelectric speaker.

CONSTITUTION: When a signal generating part 5 of a membrane-shaped piezoelectric speaker 6 is touched with the finger, the signal is generated by the piezoelectric characteristic or the pyroelectric characteristic of a piezoelectric membrane 10. The output of the signal generating part 5 is inputted through an always closed switch 7 to a comparator 8, compared with the set value, and at the time of the set value above, the operating signal is outputted from this. The set value is set to the value of the safe side by either of the value in which the comparator 8 is operated by the signal to occur at the signal generating part 5 due to the body temperature by touching with the finger and is not operated by the signal to occur at the signal generating part 5 by the ambient temperature, and the value in which the comparator is operated by the signal to occur at the signal generating part 5 when the pressure due to the touching of the finger and so on is applied and not operated by the signal to occur at the signal generating part 5 by the vibration of the circumference, and so on, and the erroneous action is prevented.