In a portable small size printer unit 1, when a pickup roller is replaced, user grips a roller main body and slides it resisting a bias force of a spring. Consequently, when the roller main body is slid, the entire length of the pickup roller is shortened, so that a first convex portion is removed from a first concave portion. After that, the front end of a slide shaft member is removed from a shaft mounting portion by tilting the roller main body and then, the pickup roller is removed from the printing mechanism unit. By sliding the slide shaft member outward of the roller main body, the roller main body is taken out of the slide shaft member and the like so as to replace only the roller main body.