A radar-installation-angle calculating device for a radar apparatus mounted on a front-side portion of a vehicle, the radar-installation-angle calculating device comprising: a radar data acquisition circuitry that generates a first data group and a second data group for each frame of a plurality of frames by using information regarding a velocity of the vehicle and a moving direction of the vehicle Θ V relative to the forward direction, which is the straight-ahead direction, the first data group indicating a plurality of reflection wave intensities from a plurality of reflection points with respect to radar directions and distances from the radar apparatus to the reflection points, the second data group indicating Doppler velocities of the reflection points with respect to the radar directions and the distances from the radar apparatus to the reflection points, and the radar directions indicating directions in which the corresponding reflection points exist relative to the radar apparatus; data selection circuitry that generates a third data group by using the first data group and the second data group, the third data group indicating the reflection wave intensities from the reflection points with respect to the radar directions and the Doppler velocities; radar movement estimation circuitry that calculates a radar moving direction Θ s, which is the moving direction of the vehicle Θ V relative to a radar axis direction for each of the plurality of frames, based on the third data group, the radar moving direction Θ s indicating a moving direction of the radar apparatus relative to the moving direction of the vehicle Θ V; and calculation circuitry that estimates the radar moving direction Θ s in a state in which the moving direction of the vehicle Θ V is straight ahead, by using the radar moving direction Θ s relative to the moving direction of the vehicle Θ V in a determined number of frames of the plurality of frames, and that calculates a radar installation angle β by using the estimated radar moving direction, characterized in that the radar movement estimation circuitry calculates, for each of the plurality of frames, the radar moving direction Θ s based on the third data group by using a value obtained by adding 90 degrees to the radar direction in which the Doppler speed is equal to zero, and calculates a plurality of sample points of the radar moving direction Θ s with respect to the moving direction of the vehicle Θ V, when the moving direction of the vehicle Θ V is within a range of predetermined angles with respect to the state in which the moving direction of the vehicle Θ V is straight ahead, the calculation circuitry estimates the radar moving direction Θ s in the state in which the moving direction of the vehicle Θ V is straight ahead by performing linear regression based on the plurality of sample points. a radar data acquisition circuitry that generates a first data group and a second data group for each frame of a plurality of frames by using information regarding a velocity of the vehicle and a moving direction of the vehicle Θ V relative to the forward direction, which is the straight-ahead direction, the first data group indicating a plurality of reflection wave intensities from a plurality of reflection points with respect to radar directions and distances from the radar apparatus to the reflection points, the second data group indicating Doppler velocities of the reflection points with respect to the radar directions and the distances from the radar apparatus to the reflection points, and the radar directions indicating directions in which the corresponding reflection points exist relative to the radar apparatus; data selection circuitry that generates a third data group by using the first data group and the second data group, the third data group indicating the reflection wave intensities from the reflection points with respect to the radar directions and the Doppler velocities; radar movement estimation circuitry that calculates a radar moving direction Θ s, which is the moving direction of the vehicle Θ V relative to a radar axis direction for each of the plurality of frames, based on the third data group, the radar moving direction Θ s indicating a moving direction of the radar apparatus relative to the moving direction of the vehicle Θ V; and calculation circuitry that estimates the radar moving direction Θ s in a state in which the moving direction of the vehicle Θ V is straight ahead, by using the radar moving direction Θ s relative to the moving direction of the vehicle Θ V in a determined number of frames of the plurality of frames, and that calculates a radar installation angle β by using the estimated radar moving direction, characterized in that the radar movement estimation circuitry calculates, for each of the plurality of frames, the radar moving direction Θ s based on the third data group by using a value obtained by adding 90 degrees to the radar direction in which the Doppler speed is equal to zero, and calculates a plurality of sample points of the radar moving direction Θ s with respect to the moving direction of the vehicle Θ V, when the moving direction of the vehicle Θ V is within a range of predetermined angles with respect to the state in which the moving direction of the vehicle Θ V is straight ahead, the calculation circuitry estimates the radar moving direction Θ s in the state in which the moving direction of the vehicle Θ V is straight ahead by performing linear regression based on the plurality of sample points.