A secondary battery is charged at a predetermined charging current density to a first SOC, and discharged at a discharging current density same as the charging current density to a second SOC smaller than the first SOC, the voltage thereof is stabilized by leaving the secondary battery for a predetermined time while maintaining the secondary battery in the range of ±3° C. from the battery temperature of the secondary battery that has been discharged, the secondary battery the voltage of which has been stabilized is self-discharged under room temperature, and the presence or absence of a short-circuit is detected on the basis of a voltage drop amount after a given time.