A machining simulation device includes a local-region setting unit that sets a local region for a workpiece, an offset-deformation processing unit that offsets and deforms a shape of a part of a whole three-dimensional shape model of the workpiece, for which the local region is set, and generates a local three-dimensional shape model of the workpiece, a local tool-movement-data output unit that outputs local tool movement data from whole tool movement data based on a tool model and movement path data of a tool, a local cutting-deformation processing unit that cuts and deforms the local three-dimensional shape model of a workpiece based on the local tool movement data, and a display superimposing unit that superimposes the cut and deformed local three-dimensional shape model of the workpiece on the whole three-dimensional shape model of the workpiece, and displays the superimposed result.