A printer apparatus in which printing is performed on a printing medium (B, S) by ejecting ink while a printer head is relatively moved in a feeding direction and a scanning direction perpendicular to each other in a faced state with respect to the printing medium supported by a medium support means for supporting the printing medium, comprising: a feeding mechanism which includes a feed roller that is extended in a right and left direction at a height position substantially same as an upper face of the medium support means and is rotationally driven, and a plurality of roller assemblies in which rotatable pinch rollers arejuxtaposedly disposed in the right and left direction on an upper side of the feed roller, the feeding mechanism pinching the printing medium (B, S) placed on the medium support means between the feed roller and the pinch rollers to feed the printing medium (B, S) in a front and rear direction; a head moving mechanism for moving the printer head in the scanning direction; and a print control section for executing feed control of the printing medium by the medium feeding mechanism and movement control of the printer head by the head moving mechanism; wherein the roller assembly is structured of an assembly main body, a clamp base and a roller member which includes the pinch roller and is attachable / detachable with respect to the assembly main body; wherein the roller member pivotally supports the pinch roller so as to be rotatable by a roller pin, characterized by the fact that: the roller member is attached to a tip end part of the clamp base with a recessed part which is provided in the roller member and fitted to a fixed shaft of the clamp base; and wherein a clamp state can be changed by exchanging the roller member depending on material and/or thickness of the printing medium. a feeding mechanism which includes a feed roller that is extended in a right and left direction at a height position substantially same as an upper face of the medium support means and is rotationally driven, and a plurality of roller assemblies in which rotatable pinch rollers arejuxtaposedly disposed in the right and left direction on an upper side of the feed roller, the feeding mechanism pinching the printing medium (B, S) placed on the medium support means between the feed roller and the pinch rollers to feed the printing medium (B, S) in a front and rear direction; a head moving mechanism for moving the printer head in the scanning direction; and a print control section for executing feed control of the printing medium by the medium feeding mechanism and movement control of the printer head by the head moving mechanism; wherein the roller assembly is structured of an assembly main body, a clamp base and a roller member which includes the pinch roller and is attachable / detachable with respect to the assembly main body; wherein the roller member pivotally supports the pinch roller so as to be rotatable by a roller pin, characterized by the fact that: the roller member is attached to a tip end part of the clamp base with a recessed part which is provided in the roller member and fitted to a fixed shaft of the clamp base; and wherein a clamp state can be changed by exchanging the roller member depending on material and/or thickness of the printing medium. the roller member is attached to a tip end part of the clamp base with a recessed part which is provided in the roller member and fitted to a fixed shaft of the clamp base; and wherein a clamp state can be changed by exchanging the roller member depending on material and/or thickness of the printing medium.