By providing an apparatus unit replacement assisting method, in which, upon receipt of a request from a first user to replace a first unit comprising part of an apparatus with a second unit, the second unit is offered to the first user at a price after the deduction of the trade-in price of the first unit, and maintenance is performed on the first unit taken from the first user for trade-in, so that the first unit in maintenance status is offered to a second user who wishes replacement with the first unit at a price lower than the price of the first unit when newly purchased, it is possible to reduce the cost incurred when replacing a unit in a CT apparatus or the like on the part of the user, such as a hospital, and facilitate the management of the production line of the apparatus and the dispatch of service persons on the part of the manufacturer while making a contribution to environmental improvement.