A state detecting method and device of a secondary battery correct impact resulting from state quantities caused by variation and calculate a state of charge with high accuracy. The state detecting method includes a first step of acquiring a detected voltage value and a detected current value, a second step of acquiring state quantities caused by variation such as a detected temperature value, a third step of determining if the detected voltage value is the voltage threshold value or greater, a fourth step of determining if the detected current value is the current threshold value or less, a fifth step of determining if a duration time of the current threshold value or less has elapsed a determination time, a sixth step of setting a state of charge in a reference state as the state of charge, and a seventh step of correcting the state of charge in the reference state.