1. A program visualization device for visualizing a program in units of modules included in a source code of the program, comprising: processor and associated memory components configured as: a source code acquisition unit for acquiring the source code to be visualized; a word data acquisition unit for acquiring word data described in the source code itself or in another source code or data related to the source code; a viewpoint information storage unit configured to associate and store viewpoint information that is to be noted in visualizing the modules and a viewpoint relevance threshold set for each piece of viewpoint information; a keyword storage unit configured to store, as a keyword, the word data that the word data acquisition unit has acquired from the source code based on the viewpoint information stored in the viewpoint information storage unit; a per-module viewpoint relevance determination data storage unit configured to store a viewpoint relevance set for each of the modules; an action determination table that associates and stores an item used for calculating a viewpoint relevance of each of the modules and viewpoint relevance weight data that is a weighting factor related to the viewpoint relevance; a viewpoint relevance weight data storage unit of an inter-module path configured to associate and store an inter-module call path used for calculating the viewpoint relevance of each of the modules and a viewpoint relevance weight data set for each inter-module call path; a module call relationship extraction unit for extracting a module call relationship indicative of a call relationship between modules included in the source code; a data analysis unit for calculating, for each of the extracted modules, a viewpoint relevance and storing the calculation result into the per-module viewpoint relevance determination data storage unit in consideration of a viewpoint relevance weight related to the call relationship between modules with a viewpoint dependent module as a base point, which is a module extracted using a keyword corresponding to the viewpoint information stored in the viewpoint information storage unit or a viewpoint relevance weight related to a common data usage relationship recorded in the action determination table; a module extraction unit for extracting a module from inside the source code; a visualization determination unit configured to determine whether or not to visualize the module extracted from the source code, by comparing the viewpoint relevance of each of the modules stored in the per-module viewpoint relevance determination data storage unit and a viewpoint relevance set in a corresponding keyword stored in the viewpoint information storage unit; a viewpoint relevance determination correction information storage unit configured to associate the viewpoint relevance set for each of the modules with a determination item, a determination condition, the viewpoint information, a determination threshold, and a viewpoint relevance correction value for correcting a criterion to determine whether or not to visualize the module, and store as viewpoint relevance determination correction information; and a viewpoint relevance correction unit configured to compare a value of the calculated viewpoint relevance with a threshold acquired from the viewpoint relevance determination correction information storage unit or a threshold specified by a user to acquire a corresponding viewpoint relevance correction value, with respect to a module whose viewpoint relevance has been calculated, correct the viewpoint relevance using the viewpoint relevance correction value, and store a correction result into the per-module viewpoint relevance determination information storage unit; and a display unit configured to display the module, which the visualization determination unit has determined to visualize, in a predetermined format.