An area machining method for machining an area defined by an outline curve. To machine the inside of an area defined by an outline curve (OLC) consisting of a multiplicity of straight lines (S1, S2, ... S6) and a circular arc (A1), the method includes: a step of approximating a circular arc portion (A1') of an offset curve (OFC) which is a predetermined amount offset from the outline curve by straight lines; a step of dividing the area defined by the offset curve which is approximated by the straight lines into a plurality of convex polygons (PG1 to PG3); a step of calculating the centroid (Wi) of each of the convex polygons and respective middle points (M1, M2) of boundary lines (B1, B2) between two convex polygons adjacent to each other, and generating a base line (BL) formed by successively connecting together the centroids and the middle points; a step of dividing into a predetermined number of sections each of the straight lines (L1 to L14) which respectively connect the centroids (Wi) of the convex polygons and the apexes (P1 to P10) of the convex polygons and each of the straight lines (BL1 to BL4) which respectively connect the middle points (M1, M2) and corresponding endpoints (P1, P4; P4, P7) of the boundary lines halved by the respective middle points; a step of moving a tool along a plurality of closed paths (CPT1, CPT2 ... ) obtained by connecting together partition points (Pa1, Pa2 ... Pa18; Pb1, Pb2 ... Pb18) corresponding to the straight lines (L1 to L14, BL1 to BL4) such that the closed paths surround the base line (BL), and moving the tool along the base line (BL); and moving the tool along the offset curve (OFC).