To prevent an opening of a printing head from being dried by letting a cap automatically closed even when an operator forgets to close the cap after a printing operation.

When a small printing device 1 with a cap 21 opened is swept to a medium to be printed, a character image is formed on the medium with the use of a liquid ink based on a change in a relative position of a printing head 13 and the medium. After data of a character string are finished to be printed thereby to completely form the character string, a print control circuit turns off a solenoid 33, so that a driving shaft 33a butting to a projection 31 is moved from the present position to a position separated from the projection 31. A lever 23 is consequently moved to a position to close the cap 21 by a tensile force of a coil spring 35. As a result, the cap 21 coupled by a bar 25 is closed and an opening of the printing head 13 is covered.