A battery state estimating device periodically estimates a battery state of a secondary battery. The battery state estimating device has a current amount acquiring section, a threshold amount memory, a current amount comparing section, a cycle setting section, and a battery state estimating section. The current amount acquiring section acquires a current amount flowing in the secondary battery. At least one current threshold amount is stored in advance in the threshold amount memory. The current amount comparing section compares the current amount acquired by the current amount acquiring section with the current threshold amount stored in the threshold amount memory. The cycle setting section sets an estimation cycle for estimating the state of the secondary battery based on this comparison result. The battery state estimating section periodically estimates the battery state of the secondary battery based on the estimation cycle set by the cycle setting section.