PURPOSE: To detect the setting position, width (beginning edge and terminating edge), abnormality of printing paper, etc. by adding a printing paper detection mechanism on both ends of a printing head.

CONSTITUTION: A paper detecting mechanism 2, 3 is provided on a printing head 1 and a printing paper 5 is set between a platen 4 and the printing head 1. The printing head 1 moves from the first physical printing position (a) to the horizontal direction and detects the beginning edge (b) of printing paper by a sensor 2. After this process, the printing head 1 calculates the first printing position (c) of the printing paper and the printer shifts the printing head 1 to a position (c) horizontally without the interposition of a host unit or an operator so that printing is begun.