An active energy irradiation device includes: an active energy irradiation unit having an emitting surface extending in both a first direction and a second direction, the emitting surface configured to emit an active energy ray to one side in a third direction; an inert gas supply unit having a spray port located on one side in the second direction with respect to the emitting surface, the spray port configured to spray an inert gas to the one side in the third direction; and a structure including a protrusion portion located on the other side in the second direction with respect to the emitting surface, the protrusion portion protruding to the one side in the third direction with respect to the emitting surface. A width in the second direction of the protrusion portion is larger than a width in the third direction of the protrusion portion.