The analog data representing a value measured of a product by means of a measuring device such as a vernier calipers is converted into digital data by an analog-to-digital converter. A CPU incorporates the digital data into a data message. The CPU is driven by a clock signal output from a quartz crystal oscillator. A first frequency divider divides the clock signal, thus generating a signal of a first frequency, and a second frequency divider divides the clock signal, thereby generating a signal of a second frequency. During the duration of each digital data signal at the "0" (low) level, the CPU generates a signal at the "low" or "high" level, in accordance with the signal generated by the first frequency divider. Similarly, during the duration of each digital data signal at the "1" (high) level, the CPU generates a signal at the "low" or "high" level, in accordance with the signal generated by the second frequency divider. The signals generated by the CPU are supplied to a transmitter. The transmitter transmits these signals to an external apparatus, in the form of a radio message.