A jacket having a buoyancy compensating function has a pocket into which a weight can be inserted and a flap. A first locking member is attached to outer surface of the pocket and a second locking member adapted to be engaged with the first locking member is attached to outer surface of the flap. The second locking member comprises a pair of elastic arms adapted to be guided along grooves of the first locking member and stopper means adapted to be forced into a space defined between these elastic arms and thereby to prevent the elastic arms from being elastically deformed. The weight is provided with a band strip adapted to extend outward from the pocket through a gap defined between the first locking member and the stopper means after the weight has been inserted into the pocket.