Abstract: A behavior determination device includes a measurement data receiving device configured to acquires measurement data indicating a pressure or a force measured by one or a plurality of sensors provided on a sole surface of a user's foot, a data analyzing device configured to analyze the measurement data, to identify one load phase in which the user makes one step, and calculate a plantar pressure parameter and a time parameter for every one load phase, and a behavior determining device configured to detect a peak point where a maximum local maximum is obtained for every predetermined time, based on the plantar pressure parameter and the time parameter, and determine a behavior of the user based on the peak point.