A plate fixed to a recording drum is irradiated with a laser beam emitted from an objective lens of a recording head, to generate gas. The recording head has a gas diffusion/suction unit forming an air stream in front of the objective lens. Further, a second suction unit elongated along the rotational axis of the recording drum is arranged between a transport unit supplying the plate to the recording drum and the recording head. Thus, it is possible to prevent the gas not only from contaminating the objective lens but also from diffusing in a housing following rotation of the recording drum. Consequently, an image recorder employing a photosensitive material generating gas in reaction to heat resulting from the laser beam emitted from the recording head can minimize contamination of the recording head, the transport unit etc. arranged in the housing of the apparatus with the gas.