Test environmental programs are prepared using the following steps: Upon application of H/W specification information containing information on the system architecture, a guidance is displayed based on the H/W specification information and the user is caused to input subsystem definition information. The H/W specification information and the subsystem definition table are related to each other to prepare the specification description of system architecture, which is used together with the simulator in a simulator library to generate test environment programs according to a testee designation. In the application-specific hardware simulator, a hardware simulation model simulating the I/O device behavior is prepared as follows: An internal connection analysis table and a definition table defining various system architectures are prepared from the hardware description information describing the I/O device hardware specification in the specification description language. An external I/O interface definition table is thus prepared from an I/O device hardware specification, an interface routine for data conversion between the I/O device and the application-specific hardware simulator and information from the user for designating the correspondence between the I/O device and the interface routine. These various tables are used to generate a source program for the hardware simulation model.