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.