To provide a buoyancy controller enabling the use of a weight without a fixing means to a pocket and the easy extraction of the weight from the pocket.

The jacket of this buoyancy controller comprises the pocket 29 allowing the weight 51 to be inserted therein and a flap 23. A first lock member 41 is installed on the outer surface of the pocket 29, and a second lock member 42 engageable with the first lock member 41 is installed on the outer surface of the flap 23. The second lock member 42 comprises a pair of elastic arms 73 and 74 allowed to advance into the grooves 62 and 63 of the first lock member 41 and a stopper means 78 advancing between these elastic arms 73 and 74 and stopping the deformation of the elastic arms 73 and 74. The weight 51 inserted into the pocket 29 comprises a band piece 53 extensible to the outside of the pocket 29 through a clearance between the first lock member 41 and the stopper means 78.