PURPOSE: To supply electric power condensed as required to a contact detection part and a transmitting body by providing a constant voltage control circuit to control the electric power of a condenser to specified voltage at the time of supplying the electric power to the condenser to condense electric power of a solar battery, the contact detection part and the transmitting body.

CONSTITUTION: At the time when a touch sensor stands by at a magazine, one circuit of an electric power source switch 52 is closed and the other circuit is opened, and no electric power is supplied to an oscillating part 59, an amplifying part 60 and a transmitting part 50. However, a solar battery is generated by irradiation in a plant and other lightings. At this time, electric power condensed in a condenser 54 by a constant voltage control circuit 55 is controlled to be necessary voltage. Thereafter, the other circuit of the electric power source switch 52 is closed, and electric power of this condenser 54 is supplied to the oscillating part 59, the amplifying part 60, the transmitting part 50 and a contact detection part 11.