A microcomputer includes therein an operation control part which can be operated when a clock signal is applied thereto by an oscillation circuit. If the operation control part reads out an identification code from an EEPROM, then it switches a control signal to be given to a switching element in accordance with the levels of the respective bits. When the control signal is off, the oscillation frequency of the oscillation circuit is F1. On the other hand, if the control signal is turned on, then one terminal of a capacitor is grounded to thereby switch the oscillation frequency over to F2. The clock signal is divided by a frequency dividing circuit before it is output. The frequency of the output signal after being divided becomes f1 or f2 in accordance with the above switching and the output signal is transmitted in the form of a frequency modulation signal.