A computer program, method, and apparatus that manage reservation of IT resources for efficient use thereof. Upon receipt of a reservation request, an IT resource finder identifies IT resources that are available for reservation in a period specified in the request. Subsequently a vacant period finder identifies vacant periods containing the specified reservation period, based on the reservation records of each IT resource. Out of the found vacant periods, an idlest period selector then selects an idlest period that offers a largest number of available IT resources. From among a set of IT resources whose vacant periods agree with the idlest period, an IT resource selector selects an appropriate resource to serve the given reservation request. A reservation registration processor then registers the reserved IT resource with the reservation data repository as determined by the IT resource selector.