According to the present disclosure, a state estimation device estimating a state of a monitoring target based on an involuntary eye movement of an eyeball of the monitoring target is provided. The state estimation device in the present disclosure includes a microsaccade information acquisition portion obtaining microsaccade information that includes a state of variation of a gaze angle when a microsaccade of the involuntary eye movement occurs, and a state estimation portion estimating the state of the monitoring target based on the microsaccade information.