PURPOSE: To measure and conserve accurate electric energy, by returning electric energy to normal when the abnormal value of an integral pulse value returns to the normal value.

CONSTITUTION: For example, an abnormal integral pulse value is inputted at time t122. At this time, a reference value is denoted as P0, an integral pulse value at time t121 as P121, an integral value at time t121 as W121, and an integral pulse value at time t122 as P122; and an integral value W122 at time T122 is An integral pulse value at time t123 in a next period is denoted as P123, and an integral value W123 at time t123 is found. In this case assuming as, P123>P121, (P123-P121)<P0/2, and P122<P121. Then, W123=W121+ P122-P121+P123-P122= W121-P121-P123 is obtained, where W123 is an integral value between time t121 and time t123, so the integral pulse value P122 at time t122 is made irrelevant.