4. An automatic music composing apparatus as claimed in claim 2, in which said substitution means includes means to substitute another sentence within the musical template for the sentence in the same musical template in comparison with the corresponding sentence in the composition conditions, and said predetermined rule is that a sentence symbol in the musical template is substitutable for the corresponding sentence symbol in the composition conditions, when said sentence symbol in the musical template is identical to or similar to said corresponding sentence symbol in the composition conditions, after the substitution of the sentence in the musical template.
4. An automatic music composing apparatus as claimed in claim 2, in which said substitution means includes means to substitute another sentence within the musical template for the sentence in the same musical template in comparison with the corresponding sentence in the composition conditions, and said predetermined rule is that a sentence symbol in the musical template is substitutable for the corresponding sentence symbol in the composition conditions, when said sentence symbol in the musical template is identical to or similar to said corresponding sentence symbol in the composition conditions, after the substitution of the sentence in the musical template. 5. An automatic music composing apparatus as claimed in claim 4, in which said substitution means includes means to exchange the aligned position of the sentences in the musical template.