1. A fuzzy control apparatus in which a rule may be changed, comprising: fuzzy reasoning means in which a rule may be changed during operation; means for storing a fuzzy reasoning output which prevails immediately prior to a rule change; synthesizing output means for combining, and outputting as a fuzzy-control output, the stored fuzzy reasoning output which prevailed immediately prior to the rule change and a fuzzy reasoning output which prevails following the rule change, said synthesizing means combining the stored fuzzy reasoning output which prevailed immediately prior to the rule change with said fuzzy reasoning output which prevails following the rule change using a combining ratio; and means for altering said combining ratio with passage of time from a moment at which the rule change is made such that there is a gradual decrease in a percentage of the fuzzy reasoning output which prevailed immediately prior to the rule change, and a gradual increase in percentage reasoning output which prevails following the rule change, in the fuzzy-control output of said synthesizing output means, and for outputting, as the fuzzy-control output, and upon passage of a predetermined time from the moment at which the rule change is made, the fuzzy reasoning output which prevails following the rule change.