A hysteresis characteristic unit switches between outputs of selection instructions in accordance with a status characteristic depending on a present selection state (history). Specifically, the hysteresis characteristic unit makes determination of switching in accordance with the status characteristic if the selection instruction has been selected, and makes determination of switching in accordance with the status characteristic if the selection instruction has been selected. If a charge/discharge voltage is lower than a charge/discharge voltage by an amount exceeding a switching threshold voltage, switching from the selection instruction to the selection instruction is made.