An air supply and exhaust system used for a buoyancy compensator includes an air supply and exhaust unit attached to a jacket, a manipulating unit connected to a hose extending from an air cylinder and first and second hoses connected to these two units. The air supply and exhaust unit uses the air supplied from the manipulating unit to supply the air to the jacket and to open an air exhaust valve and thereby to exhaust the air from the jacket. The manipulating unit uses a rotary change-over switch to supply the air from an air cylinder to a main supply pipe or an air chamber of the air supply and exhaust unit.