A tape printing apparatus registers a word string constituting document data to be printed by depression of a print key in a learnt-contents storing region under subscribed conditions. A CPU divides the document data to be printed into letter strings based on information about constituent letters of the to-be-printed word string and a learning condition determination table. Thereafter, the CPU determines whether or not the to-be-printed word string should be registered based on registered letter string data stored in the learnt-contents storing region and the contents of the divided letter string.