WATTMETER

PROBLEM TO BE SOLVED: To provide a wattmeter facilitating the observation of instantaneous power waveform. SOLUTION: This wattmeter 1 is provided with a first polarity inverting circuit 2 for inverting the polarity of an input signal synchronously with a first clock of specified frequency, a second polarity inverting circuit 3 for inverting the polarity of an input signal synchronously with a second clock, a multiplier 4 for multiplying output signals of both polarity inverting circuits 2, 3 by each other, a third polarity inverting circuit 6 for inverting the polarity of a multiplied signal of the multiplier 4 synchronously with a third clock double the frequency of the first clock, and a smoothing circuit 7 for smoothing a polarity inverting signal of the third polarity inverting circuit 6; and the power value of object power to be measured is measured on the basis of an output signal of the smoothing circuit 7. The wattmeter of such constitution is provided with a high-pass filter circuit 5 disposed between the multiplier 4 and the third polarity inverting circuit 6 and having cut-off frequency lower than any of each predicted lowest frequency of both input signals and the frequency of the first and second clocks so as to output the polarity inverted signal of the third polarity inverting circuit 6 as a power waveform signal.