To inexpensively, highly reliably and highly accurately detect a charging/discharge current of a secondary battery mounted on an electric vehicle or the like.

A voltage signal generated to a current detection resistance 21 connected in series to a battery pack 20 is transmitted by a transmitting means 28 to the battery ECU 22. The voltage signal is detected as a pulse signal by a discharge current detection part 221, a first capacitor 222 and a pulse generation part 223 at a discharge time when the battery pack discharges. The voltage signal is detected as a pulse signal by a charging current detection part 224, a second capacitor and a pulse generation part 226 at a charging time when the battery pack is charged. The pulse signals at the discharge time and the charging time are calculated at event counters 2271 and 2272 as the current of the battery pack.