1. A fuzzy retrieval apparatus comprising: a data base in which a plurality of types of attribute signals with respect to an item of a plurality of items are registered in advance for each item; means for setting signals representing a retrieval condition which comprises at least two preconditions each indicating a desired condition relating to at least one of the plurality of types of the attribute signals, and a connecting condition that connects these preconditions; membership operating means for producing degree-of-membership signals that indicate the degrees to which an attribute signal conforms to set preconditions; MEAN operating means for producing and outputting a signal indicating a mean value of a plurality of applied degree-of-membership signals; MIN operating means for selecting and outputting a signal, which indicates a minimum value, from a plurality of applied degree-of-membership signals; MAX operating means for selecting and outputting a signal, which indicates a maximum value, from a plurality of applied degree-of-membership signals, and control means for applying the degree-of-membership signals obtained from the membership operating means to at least one of the MEAN operating means, MIN operating means and MAX operating means in accordance with a predetermined connecting condition, and outputting a degree-of-concurrence signal obtained from a final stage of at least one of the MEAN operating means, MIN operating means and MAX operating means.