INK JET PRINTER

To accurately measure length of the printing region of a transparent recording medium.SOLUTION: A printer 10 has: a platen 16 placed with a transparent recording medium 5; a pair of restriction members 90 restricting floating up of both end parts in a main scanning direction Y of the recording medium 5 placed on the platen 16; an optical sensor 31 provided movably in the main scanning direction Y above the recording medium 5 placed on the platen 16 and the restriction members 90 and irradiating light and receiving reflectance; and a control device 80 connected to the optical sensor 31. Colors of the platen 16 and the restriction members 90 are different from each other. The control part 80 measures a length LX in the main scanning direction Y of a printing region of the recording medium 5, on the basis of a first light receiving amount of light reflected in the pair of the restriction members 90 when the optical sensor 31 moves in the main scanning direction Y while irradiating the light, and a second light receiving amount of light passing through the recording medium 5 and reflected in the platen 16.SELECTED DRAWING: Figure 6 【課題】透明な記録媒体の印刷領域の長さを精度よく測定すること。【解決手段】プリンタ１０は、透明な記録媒体５が載置されるプラテン１６と、プラテン１６に載置された記録媒体５の主走査方向Ｙの両端部の浮き上がりを抑制する一対の抑制部材９０と、プラテン１６に載置された記録媒体５および抑制部材９０上を主走査方向Ｙに移動可能に設けられ、光を照射しかつ反射光を受光する光学センサ３１と、光学センサ３１に接続された制御装置８０と、を備え、プラテン１６の色と抑制部材９０の色とは異なり、制御装置８０は、光を照射させながら光学センサ３１が主走査方向Ｙを移動したときの一対の抑制部材９０において反射した光の第１受光量と記録媒体５を透過してプラテン１６において反射した光の第２受光量とに基づいて、記録媒体５の印刷領域の主走査方向Ｙの長さＬＸを測定する。【選択図】図６