An OS image shrinking apparatus for shrinking a size of at least one OS image stored in a computer. The OS image shrinking apparatus includes an execution history management unit that operates a predetermined application program on the computer for a predetermined time and manages an execution history of a function by monitoring the function executed during operation of the application program, a saved function management unit that refers to the execution history managed by the execution history management unit and manages the function existing in the execution history, as a saved function, among functions included in the OS image, and an unused function processing unit that performs a processing to delete from the OS image a function not managed by the saved function management unit, as an unused function, among the functions included in the OS image.