In a slant cutting method in which a cutting torch is slanted to cut a workpiece to trim a product, the cutting lines on the downstream side and on the upstream side are respectively extended at the intersecting portion, and the cutting torch is pivotally moved in a direction such that the pivot angle is made smaller when cutting direction of the cutting torch is changed toward the extended line of the cutting line at an end point as cut along the extended line. The cutting period and the area size of scraps can be reduced with this slant cutting method.