A housed gyro-sensor 31 is housed in a rotation plate 33. The gyro-sensor 31 is mounted so that a rotation operation is enabled in a pitch axis direction about an axis in a mounting hole 24 formed on a housing of an inner face of the car navigation system 21. In this way, as shown in FIG. 8, even when the main body of the car navigation system 21 is not housed horizontally with respect to the vehicle, it is possible to regulate the mounting angle of the housed gyro sensor 31 in a horizontal direction by rotating the rotation plate 33. In order to realize how many times the rotation plate 33 needs to be rotated, standards for angle settings may be provided by directly printing the name of the vehicle type on an outer face of the rotation plate 33 or by printing the major angles.