1. A machining simulation device that simulates cutting work on a workpiece by cutting and deforming a three-dimensional shape model of the workpiece based on a tool model and movement path data representing a movement path of a tool, and displaying the cut and deformed three-dimensional shape model of the workpiece, the device comprising: a holding unit that holds therein the three-dimensional shape model of the workpiece after the cutting work; a unit that sets a local region for the workpiece; a unit that offsets and deforms a shape of a part of the three-dimensional shape model of the workpiece after the cutting work, for which the local region is set, by a predetermined thickness in an outward direction, and generates a local three-dimensional shape model of the workpiece; a tool-movement-data generation unit that generates whole tool movement data based on the tool model and the movement path data of the tool; a local tool-movement-data output unit that outputs local tool movement data that are tool movement data obtained when the tool passes through the local region from the whole tool movement data; a local cutting-deformation processing unit that cuts and deforms the local three-dimensional shape model of the workpiece based on the local tool movement data; and a unit that displays a superimposed three-dimensional shape model obtained by superimposing the local three-dimensional shape model of the workpiece, which has been cut and deformed by the local cutting-deformation processing unit, on the three-dimensional shape model of the workpiece obtained after the cutting work, which has been held in the holding unit.