The present invention reduces an arithmetic operation amount for updating a state vector. The attitude estimating device includes (i) a gravitational direction estimating section for updating, by using an acceleration vector as an observation, a gravitational direction vector predicted from an angular velocity vector, (ii) a horizontal direction estimating section for updating, by using a magnetic vector as an observation, a horizontal direction vector predicted from the angular velocity vector, and an attitude estimating section for generating attitude information with use of the gravitational direction vector and the horizontal direction vector.