[Summary][Objective] Estimation accuracy in a battery status estimating device which estimates a charge status of a secondary battery should be improved further more.[Means for Solution] In an SOC estimation by integration of a charge-and-discharge current, influence of a sensor error cannot be disregarded, and the influence of such an error is accumulated as time passes. On the other hand, in an SOC estimation based on measured values of a battery voltage and a battery temperature, estimation accuracy largely depends on a load-generation pattern. Then, in accordance with the present invention, by mixing both, while one of them is reset based on a reliability in accordance with an operation situation and/or an input current value which will be the premise for an SOC estimate calculation in a battery model is set up based on the reliability, it becomes possible to compute an SOC estimate in high accuracy as much as possible in accordance with the operation situation.