A cooler (144) providing gas blows and comprising at least one cooler module having at least one cooler module (41, 42, 43, 44) of the cooler (144) is curved to provide a gas turn module for turning run of the fiber web (W) from its main running direction 80-190°. The cooler (144) includes moisturizing at least one surface of the fiber web. Having a blowing zone (45, 46, 53) in which gas is blown toward a surface of the fiber web and that the cooler comprises at least one suction zone (51), in which the fiber web evaporated moisture is drawn away from the proximity of a surface of the fiber web. There are cooler modules on both sides of the fiber web. The cooler has a gas turn module located inside a curved fiber web run, which provides gas blows toward the curved fiber web during the run.