An air cooling apparatus having a cooler including a plurality of fins arranged in substantially parallel relationship with a predetermined spacing therebetween and heat transfer tubes extending through the fins in a plurality of positions in the fins is further provided with at least one defrosting device having a plurality of projecting members of a width slightly smaller than the spacing between the fins which projecting members are each located between the adjacent two fins. The defrosting device is mounted for rotation about the heat transfer tubes and operative to remove frost from the surfaces of the cooler while rotating which frost has been formed during the operation of the air cooler.