When rotating a recording drum at low speed, air is jetted from air jet ports toward a point of irradiation, in a direction to diffuse a gas generating from an image recording medium upstream with respect to a direction of rotation of a recording drum. An air curtain approximately semicircular about the point of irradiation is formed upstream thereof with respect to the direction of rotation of the recording drum. As a result, the gas can hardly diffuse from the point of irradiation upstream with respect to the direction of rotation of the recording drum. The gas is collected from a gas suction opening. Thus, the gas is reliably prevented from contacting the image recording medium having an image recorded thereon.