A path calculation program for calculating in a computer apparatus a tool path for processing a curved processed part formed by a hole provided in a curved-surface-shaped workpiece, the hole including a thick internal surface, the program causing the computer apparatus to function as: a workpiece shape information inputter configured to input workpiece shape information about a shape of the workpiece and a shape of the curve; a tool shape information inputter configured to input tool shape information about a shape of a tool; a first tangent vector calculator configured to calculate a first tangent vector to a curve of the curved processed part, at a specified point on the curve; an addition vector calculator configured to calculate an addition vector obtained by adding a second tangent vector, of an intersection line of a normal plane to the first tangent vector at the specified point within the thick internal surface of the hole, to a third tangent vector, of an intersection line of the normal plane with the curved surface, at a predetermined ratio, wherein each of the angle between the addition vector and the first tangent vector and the angle between the addition vector and the second tangent vector is a bisected angle of the angle between the first tangent vector and the second tangent vector; and a tool position calculator configured to calculate the tool position that is located on a straight line extending from the specified point and including the calculated addition vector, and enable the specified point to be processed by the tool based on the input tool shape information by specifying, as the position of the center point of the tool, an intersection point between a circle and a range, the circle centering on the specified point on the curve and having a radius with a length of a distance A, the range determined by intersecting a plane including the first and second tangent vectors and the shape of the workpiece, the distance A being a distance between the tool and the specified point on the curve, wherein the tool position calculator calculates the tool position with a plurality of points on the curve set as specified points to calculate the tool path. a workpiece shape information inputter configured to input workpiece shape information about a shape of the workpiece and a shape of the curve; a tool shape information inputter configured to input tool shape information about a shape of a tool; a first tangent vector calculator configured to calculate a first tangent vector to a curve of the curved processed part, at a specified point on the curve; an addition vector calculator configured to calculate an addition vector obtained by adding a second tangent vector, of an intersection line of a normal plane to the first tangent vector at the specified point within the thick internal surface of the hole, to a third tangent vector, of an intersection line of the normal plane with the curved surface, at a predetermined ratio, wherein each of the angle between the addition vector and the first tangent vector and the angle between the addition vector and the second tangent vector is a bisected angle of the angle between the first tangent vector and the second tangent vector; and a tool position calculator configured to calculate the tool position that is located on a straight line extending from the specified point and including the calculated addition vector, and enable the specified point to be processed by the tool based on the input tool shape information by specifying, as the position of the center point of the tool, an intersection point between a circle and a range, the circle centering on the specified point on the curve and having a radius with a length of a distance A, the range determined by intersecting a plane including the first and second tangent vectors and the shape of the workpiece, the distance A being a distance between the tool and the specified point on the curve, wherein the tool position calculator calculates the tool position with a plurality of points on the curve set as specified points to calculate the tool path.