To provide a power storage means controller that, when estimated SOC information is reset, brings estimated SOC close to true SOC in a shorter time.

The power storage means controller 100 includes: a charge/discharge estimating means 14 that estimates the state of charge of a chargeable/dischargeable battery 50; a memory means 16 that stores state-of-charge information from the charge/discharge estimating means 14; and a charge/discharge controlling means 18 that operates as follows depending on an event in the memory means 16 supplied with power from an accessory battery 46 as a detachable accessory power storage means: when the power supply is interrupted once and then restarted and state-of-charge information is reset, the controlling means controls charging/discharging of the battery 50 so that charging/discharging of the battery 50 is accelerated based on the state of charge estimated by the charge/discharge estimating means 14; and when it is determined that the state of charge estimated by the charge/discharge estimating means 14 has been approximated to the true state of charge, the controlling means changes charge/discharge control on the battery 50 so that the state of charge is kept in an intermediate range.