1. A program search apparatus, comprising: a program information storage unit which stores program information; an operation history storage unit which stores TV operation history which is a history of an operation of a TV performed by a user; a preference information management unit which generates preference information, which represents a preference of the user, from the program information and the TV operation history and which manages the preference information at prescribed periods; a preference change amount calculation unit which calculates an amount of change of the preference of the user using the preference information managed at prescribed periods; a weight calculation unit which calculates a weight given to the preference information from the amount of change of the preference of the user calculated by the preference change amount calculation unit; a detection unit which detects an occurrence of a change of the preference of the user using the amount of change of the preference of the user calculated by the preference change amount calculation unit; a change continuation period calculation unit which calculates a length of a period during which the preference change exists continuously; and a recommended program search unit which generates a search request by giving the weight to the preference information, the weight being calculated by the weight calculation unit and being emphasized according to the length of the period calculated by the change continuation period calculation unit, and which searches a recommended program from the program information on the basis of the search request when the occurrence of a change of the preference of the user is detected by the detection unit.