1. An automatic music composing apparatus comprising: a template data base storing a plurality of musical templates each including a set of data defining a musical piece, said musical piece being subdivided into a plurality of musical segments, said set of data including subsets of data respectively defining musical properties of said musical segments; input means for inputting composition conditions including requirements on musical properties for a musical piece to be composed; retrieval means for searching said template data base to extract at least one candidate musical template which includes said subset of data indicative of the musical properties which are identical with or similar to the musical properties required by the inputted composition conditions; and composition means for composing a musical piece based on one of said at least one extracted candidate musical template.