An acceleration acquirer of a controller of an in-bed and out-of-bed determination device acquires, in a time series, acceleration of a subject from a sensor that is an acceleration sensor attached by the subject, a body motion determiner determines, based on the acquired acceleration, whether there is a body motion of the subject at each time, an evaluator evaluates a distribution of the acceleration at a time at which it is determined that there is not a body motion, an estimator estimates a body axis of the subject based on the evaluated distribution of the acceleration, and an in-bed and out-of-bed determiner determines at least one of in bed and out of bed of the subject based on the estimated body axis of the subject that is estimated by the estimator.