A numerical control apparatus 3 comprises: a pulse generation unit 34 that moves a plurality of machine elements of a machine tool 2 along a plurality of control axes on the basis of a movement pulse for the machine tool 2; an interference checking unit 36 that performs interference checking calculation for a plurality of interference-checking subject sets; and an interference checking assistance device 5 that assists the interference checking calculation. The interference checking assistance device 5 comprises: a first storage unit 51 that stores machine element-control axis linkage information; a second storage unit 52 that stores individual axis subordinate relationship information; and a checking subject set extraction unit 54a that, on the basis of the movement pulse, the machine element-control axis linkage information, and the individual axis subordinate relationship information, extracts one or more checking subject sets from among all combinations of the machine elements.