9. A program search method, comprising: storing program information; storing TV operation history which is a history of an operation of a TV performed by a user; generating preference information, which represents a preference of the user, from the program information and the TV operation history and managing the preference information at prescribed periods; calculating an amount of change of the preference of the user using the preference information managed at prescribed periods; calculating a weight given to the preference information from the amount of change of the preference of the user; detecting an occurrence of a change of the preference of the user using the amount of change of the preference of the user; calculating a length of a period during which the preference change exists continuously; generating a search request by giving the weight to the preference information when the occurrence of a change of the preference of the user is detected, the weight being calculated from the amount of change of the preference of the user and being emphasized according to the length of the period during which the preference change exists continuously; and searching a recommended program from the program information on the basis of the search request.
9. A program search method, comprising: storing program information; storing TV operation history which is a history of an operation of a TV performed by a user; generating preference information, which represents a preference of the user, from the program information and the TV operation history and managing the preference information at prescribed periods; calculating an amount of change of the preference of the user using the preference information managed at prescribed periods; calculating a weight given to the preference information from the amount of change of the preference of the user; detecting an occurrence of a change of the preference of the user using the amount of change of the preference of the user; calculating a length of a period during which the preference change exists continuously; generating a search request by giving the weight to the preference information when the occurrence of a change of the preference of the user is detected, the weight being calculated from the amount of change of the preference of the user and being emphasized according to the length of the period during which the preference change exists continuously; and searching a recommended program from the program information on the basis of the search request. 11. The program search method according to claim 9 , further comprising generating preference information from a program name and the frequency of appearance of a genre obtained from electronic program information.