PURPOSE: To facilitate fitting and detaching a slip inserter and operate a printer irrespectively of whether or not the inserter is fitted, by a method wherein a main body of a printer is provided with an opening part for fitting slip inserter, and the opening part is covered by a slidable plate.

CONSTITUTION: When the slidable plate 2 is slidden, slip inserter engaging pins 5 fixed to a mechanism chassis incorporated in the main body 1 of the printer are exposed. Therefore, when engaging notched parts 6 provided in the slip inserter 3 are guided to the pins 5, fitting levers 7 clamp the pins 5, whereby the slip inserter 3 is fitted to the main body 1. In the condition wherein the slidable 2 is closed, noises generated by a printing head are perfectly shielded.