an acquiring unit that acquires, for each of a plurality of reflection points detected by the radar device, reflection point information including at least a horizontal angle and a vertical angle, which are azimuth angles of the reflection point that are obtained with reference to a beam direction being a direction along a central axis of a radar beam, and a distance between the radar device and the reflection point;

an extracting unit that extracts, based on at least the reflection point information, at least one road surface reflection point from among the plurality of reflection points that has been detected due to reflection by a road surface;

a device-system coordinates unit that specifies, based on the reflection point information, device-system coordinates for each road surface reflection point that represent three-dimensional coordinates based on a coordinate axis of the radar device; and

an estimating unit that estimates the axial deviation angle using a relational expression that holds between at least one unknown parameter, which includes the axial deviation angle of a coordinate axis of the radar device from a target axis which is at least one of a horizontal axis and a traveling direction axis constituting the coordinate axes of the mobile body, and at least one element included in the device-system coordinates of the road surface reflection point,

wherein the estimating unit estimates the axial deviation angle based on at least one parameter of a line approximated by a distribution of the device system coordinates of the road surface reflection points in a projection plane orthogonal to the target axis.