1. A hexahedral mesh generator which is connected to an output device, receives data of an analysis model generation target inputted thereto, and makes an analysis model by generating hexahedral mesh for the analysis model generation target, comprising: an existing analysis model database which stores data of shapes of existing analysis models before undergoing shape decomposition for the generation of hexahedral mesh and data of shapes of the existing analysis models after undergoing the shape decomposition; a shape decomposition part extracting module which compares the shape of each existing analysis model before the shape decomposition with the shape of the existing analysis model after the shape decomposition and thereby extracts a shape decomposition part as a part of the existing analysis model where the shape decomposition was executed; a shape comparison module which compares each shape decomposition part with the analysis model generation target and thereby checks whether or not the shape decomposition part coincides with at least part of the analysis model generation target; a coinciding shape decomposition part display/selection module which displays a list of the shape decomposition parts found by the shape comparison module to coincide with at least part of the analysis model generation target on the output device, receives selection of one or more shape decomposition parts from the list by the user of the hexahedral mesh generator, and outputs data of the selected shape decomposition parts; a shape decomposition module which decomposes the shape of the analysis model generation target in the same way as the shape decomposition parts outputted by the coinciding shape decomposition part display/selection module; and a hexahedral mesh generating module which generates the hexahedral mesh for the analysis model generation target after undergoing the shape decomposition by the shape decomposition module.