A user apparatus that is used in a radio communication system including a plurality of base stations, and that includes a function for performing interference reduction based on user assignment in an interference cell, including: interference pattern generation means that generates a plurality of interference patterns each of which is a combination of presence or absence of an interference signal in a given number of interference cells for the user apparatus; reception quality calculation means that calculates a reception quality after interference reduction for each of the plurality of interference patterns generated by the interference pattern generation means; and user assignment information estimation means that determines presence or absence of an interference signal in each interference cell corresponding to an interference pattern based on which the best reception quality is obtained in reception qualities calculated by the reception quality calculation means to be presence or absence of user assignment.