1. An apparatus, comprising: an associative memory in a form of a neural network, including: a plurality of nodes having activation values; and a plurality of links, connected with the nodes, having link weight values; pattern entering means for sequentially entering a plurality of learning patterns into the neural network, each learning pattern having a plurality of elements in correspondence with the nodes; energy calculation means for calculating an energy E of said each learning pattern entered by the pattern entering means; learning amount determination means for determining a learning amount .delta. for said each learning pattern entered by the pattern entering means, according to a difference between the energy E calculated by the energy calculation means and a predetermined reference energy level Eth, using the following equation: EQU .delta.=g(E-Eth) where g is an upper and lower bounded monotonically increasing function with g(0)=0; and link weight value updating means for updating the link weight values of the links according to said each learning pattern entered by the pattern entering means and the learning amount .delta. determined by the learning amount determination means.