1. A software behavior modeling apparatus, comprising: a stack information recording unit configured to obtain stack frame information for identifying a stack frame stacked on a call stack at a time when a specific event occurs in executing a software under a software execution environment, while specifying an order that the stack frame is stacked on the call stack, and to record the stack frame information in an order of an occurrence of the specific event; a termination information recording unit configured to compare, sequentially from a bottom of the call stack, (i−1)-th stack information with i-th stack information both recorded by the stack information recording unit, where i represents a natural number, and to record termination information that is a stack frame information indicating a boundary between an identical portion and a non-identical portion, where the identical portion indicates a portion where the (i−1)-th stack information and the i-th stack information are identical in terms of a position of the call stack and the stack frame information, and the non-identical portion indicates a portion following a stack frame in which the stack frame information is detected as being different between the (i−1)-th stack information and the i-th stack information; a first stack difference information generating unit configured to generate, as stack difference information, information formed by combining a portion of the (i−1)-th stack information with a portion of the i-th stack information, both portions being located from an uppermost stack frame until the termination information is detected, by using the termination information recorded by the termination information recording unit; and a model generating unit configured to generate a software behavior model based on the stack difference information.