PURPOSE: To measure the transmission power of a radio over a wide range, by measuring the absolute value of relatively large power with a first detection circuit while measuring the relative value of relatively small power with a second detection circuit.

CONSTITUTION: The reference transmission power from a transmitter 10 is detected by a detection circuit 21 and absolute data is stored in RAM of a microprocessor 27 through an A/D converter circuit 26. Next, a switch circuit 28 is connected to a detection circuit 25 and the output of the detection circuit 25, to which the reference transmission power is inputted through a frequency converter 22 and a logarithmetic amplifier 24, is stored in RAM as a reference value through the A/D converter circuit 26. Thereafter, the transmission power from the transmitter 10 is stepwise reduced and the difference from the reference value is measured at every transmission power of the transmitter 10 to operate absolute value data and decremental decibel data, and the absolute value of each transmission power reduced is calculated to be displayed on a display part 29.