To provide a printer which can operate an apparatus main body in conformity with a use environment or the like by setting a transfer width of parallel data to be transferred from a memory.

Image data input from an external apparatus via an I/F 3 is written in a memory 4 in a printer 1. The memory 4 transmits the image data to a buffer 5 with any one of transfer widths of 4 bytes, 8 bytes and 32 bytes. The buffer 5 functions as a FIFO. A shift register 6 converts and outputs the image data held in the buffer as serial data. The transfer width of image data between the memory 4 and buffer 5 can be changed in accordance with a memory capacity of the memory 4, a size of image data to be printed or the like. In other words, the printer 1 can operate in accordance with a use environment.