The present invention has an object to analyze, regarding an existing system without a source code, the relationship between input items and internal system processing with respect to output items and present the analysis results to a user. An existing system processing specification extractor is an apparatus for making an existing system operate and analogizing input items of the existing system and internal system processing patterns without performing analysis of implementation and includes: an output data change information acquisition unit that classifies changes of output data associated with input to the existing system on the basis of types of changes of each output element; and an internal system processing specifying unit that combines the classifications obtained by making different input to the existing system and specifies a type of processing based on a usage pattern of an input item value.