To provide a golf shot diagnostic device capable of comprehensively and more precisely grasping a flying distance and dispersion of right and left deflection in a golf shot.

The golf shot diagnostic device calculates, according to a plurality of flying distances and coordinate values (Dx_i, Dy_i) of right and left deflection resulting from a plurality of shots, average coordinate values (Dx_ave, Dy_ave) thereof, eigenvalues r₁ and r₂ (where r₁≥r₂) of a variance-covariance matrix thereof or square roots s₁=r₁^1/2 and s₂=r₂^1/2 thereof, and corresponding eigenvectors V₁ and V₂ to output these values. Alternatively, the golf shot diagnostic device outputs an ellipse using the point (Dx_ave, Dy_ave) as a center and having a long axis kr₁ or ks₁ in a V₁ direction and a short axis kr₂ or ks₂ in a V₂ direction (where k is a constant).