PROBLEM TO BE SOLVED: To provide a device for accurately estimating a posture of a subject, especially a standing state and sitting state, in a posture estimation device, method, and program.SOLUTION: A posture estimation device comprises: a stationary state detection unit for detecting a stationary state of a subject on the basis of a DC signal component included in output of a triaxial acceleration sensor； a movement detection unit for detecting a movement state of the subject on the basis of an AC signal component included in the output of the triaxial acceleration sensor； and a state transition detection unit for detecting a state transition of the subject on the basis of a parameter on the last movement state stored by the movement detection unit and parameters on the present and last stationary states which correspond to immediately before and after states of the last movement state and are stored by the stationary state detection unit. The posture estimation device is configured so as to calculate displacement of a tilt angle formed between a first axis direction and the gravity direction during a certain period until the end of the movement state detected by the movement detection unit, estimate that a transition is into a standing state in the case that the displacement is lower than a first value, and estimate that the transition is into a sitting state in the case that the displacement exceeds a second value larger than the first value.
