PURPOSE: To prevent a signal-originating unit requiring high power at the time of holding time for detection from consuming power to attain saving of electric power consumption, by applying for functioning a driving voltage to the signal- originating unit through a switching unit at the detecting time of a detector.

CONSTITUTION: A switching unit 2 is brought to 'ON' position by a driving signal S5 from a signal originating detecting unit 1 arranged in the neighborhood of a bath tub according to water level and water temperature. By this switched position of the switching unit 2, a driving voltage S9 is applied to a signal- originating unit 5, In this unit 5 display data have preliminarily been set which corresponded to the condition change to be detected by the detecting unit 1, and a secondary machine signal S7 is originated by application of the driving voltage S9.