A calculation device for a radar apparatus, the calculation device being configured to specify the direction of arrival of waves from a plurality of targets based on respective reception signals received at a plurality of antennae, the calculation device comprising: a calculation unit configured to use an estimation algorithm for estimating, from the respective reception signals, the arrival direction angles of the targets for a preset number of incoming waves whose arrival direction angles can be separated, hereafter referred to as a preset number of separable angles, and to generate a mode vector which models the reception signals arrived from the directions of the estimated arrival direction angles of the targets, obtained by the estimation algorithm, the calculation device being characterized in that: by the calculation unit, the mode vector is expressed in the form a θ = 1 exp − jΛdsinθ exp − jΛ 2 dsinθ..... exp − jΛ n − 1 dsinθ where j: √-1; Λ = 2π/λ, λ = wavelength; d = antenna interval; θ = estimated arrival direction angle of a target; n = number of antennae, and in that the calculation unit is further configured to respectively generate mode vectors from the estimated arrival direction angles of the targets for each of a plurality of selected numbers of separable angles from 1 to n, obtained by the estimation algorithm while sequentially changing the selected number, to calculate an orthogonal component of each of the generated mode vectors, to compare the magnitudes of the orthogonal components calculated for each of the selected numbers with a threshold, and to select, from the plurality of selected numbers of separable angles from 1 to n, the smallest value of the number of separable angles at which the magnitude of the orthogonal component of the mode vector is the threshold value or lower, as an appropriate number of separable angles. a calculation unit configured to use an estimation algorithm for estimating, from the respective reception signals, the arrival direction angles of the targets for a preset number of incoming waves whose arrival direction angles can be separated, hereafter referred to as a preset number of separable angles, and to generate a mode vector which models the reception signals arrived from the directions of the estimated arrival direction angles of the targets, obtained by the estimation algorithm, the calculation device being characterized in that: by the calculation unit, the mode vector is expressed in the form a θ = 1 exp − jΛdsinθ exp − jΛ 2 dsinθ..... exp − jΛ n − 1 dsinθ where j: √-1; Λ = 2π/λ, λ = wavelength; d = antenna interval; θ = estimated arrival direction angle of a target; n = number of antennae, and in that the calculation unit is further configured to respectively generate mode vectors from the estimated arrival direction angles of the targets for each of a plurality of selected numbers of separable angles from 1 to n, obtained by the estimation algorithm while sequentially changing the selected number, to calculate an orthogonal component of each of the generated mode vectors, to compare the magnitudes of the orthogonal components calculated for each of the selected numbers with a threshold, and to select, from the plurality of selected numbers of separable angles from 1 to n, the smallest value of the number of separable angles at which the magnitude of the orthogonal component of the mode vector is the threshold value or lower, as an appropriate number of separable angles.