To estimate the attitude angle of a mobile unit with high precision on the basis of a base line vector between GPS antennas, even when the mobile unit becomes deformed and the relative position between the GPS antennas changes.

An attack angle sensor 271, a dynamic pressure sensor 272, and a static pressure sensor 273 are installed in the body of the mobile unit. A change amount estimation section 230 acquires an attack angle , dynamic pressure q, and atmospheric pressure p from the attack angle sensor 271, the dynamic pressure sensor 272, and the static pressure sensor 273, and calculates a change amount dB of the body on the basis of the attack angle , dynamic pressure q, and atmospheric pressure p. A base line vector change amount estimation section 231 calculates a change amount dbi between the GPS antennas on the basis of the change amount dB of the body. A base line vector correction section 232 corrects the known base line vector by adding the change amount dbi. An attitude angle calculation section 220 estimates attitude angles (a roll angle , a pitch angle , and a yaw angle ) of the mobile unit on the basis of the base line vector obtained by the correction.