1. A preference learning apparatus for detecting a user's action from a portable information terminal to which various kinds of contents are provided through a communication channel and learning a user's preference on the basis of a detected action log, comprising: a content attribute information database for storing, for each content, an attribute/attribute value as objects of the learning contained in each of various kinds of contents; a action information database for storing, for each action, an attribute as an object of the learning estimated from the user's action and a weight for the attribute; a time information correlation table for storing a name and time range of a time zone in correspondence with each other; an area information correlation table for storing each area name and area range in correspondence with each other for each of a plurality of areas which classify position information of the user; a user's preference information database for storing, for each user's preference information containing an attribute/attribute value as objects of the learning, a weight for the attribute, a time zone when the weight is valid, and a place where the weight is valid; user action detection means for detecting the user's action on the basis of information obtained from the portable information terminal and acquiring detection data containing a user ID indicating the user, a action name indicating the action, a content ID indicating a content related to an object of the action, and a measurement time and position information at which the action has been detected; and preference information management means for updating said user's preference information database on the basis of preference analysis data obtained by analyzing the user's preference on the basis of the detection data output from said user action detection means, wherein said preference information management means generates the preference analysis data using time zone information acquired from said time information correlation table on the basis of the measurement time contained in the detection data output from said user action detection means, the area name acquired from said area information correlation table on the basis of the position information contained in the detection data, the attribute and weight contained in the action which are acquired from said action information database on the basis of the action name contained in the detection data, and the attribute value acquired from said content attribute information database on the basis of the attribute as an object of the learning and the content ID contained in the detection data, and updates, with the weight contained in the generated preference analysis data, the weight contained in the preference information in the user's preference information database, which is specified by the time zone information, area name, and attribute/attribute value as objects of the learning, which are contained in the generated preference analysis data, and the user ID contained in the detection data.