A drying device, which dries a photosensitive layer of a photosensitive planographic printing plate using infrared rays, includes an infrared emitting device and a filter that is arranged between the photosensitive planographic printing plate conveyed through the drying device and the infrared emitting device and that blocks a predetermined range of wavelength. More specifically, the filter is arranged between a web that is conveyed through the drying device and a mid-infrared radiator, so as to block 30% or more of wavelengths of 1 .mu.m or less. As a result, fogging on a photosensitive coating layer can be prevented, and high heating efficiency can be achieved.