PURPOSE: To facilitate the explication of the cause of an abnormal operation of a printing apparatus, by printing a printing control code and a character code as a hexadecimal internal code so as to enable the easy analysis of the abnormal operation.

CONSTITUTION: The data stored in a memory unit 1 is transferred by one byte to a one-byte data storing memory unit 2 to be stored therein, and four higher- rank bits are fetched by a fetching means 6 and shifted by four bits to the left by a four-bit shifting means 8. The result is translated into an internal code, which is stored in a printing memory unit 3. Meanwhile, four lower-rank bits are fetched by a fetching means 7, and they are translated into an internal code and stored in the printing memory unit 3. When it is determined by a printing storage capacity determining means 10 that the printing memory unit 3 is full, the stored data are printed on paper 11 by a printing mechanism 4. According to this constitution, an abnormality of a code occurring when a printing apparatus operates abnormally can be determined easily, and thus the cause of the abnormal operation can be checked up with ease.