A gas supply apparatus (21) is provided and has first and second fittings (21A,21B) and first and second tubes (10,22). The first fitting (21A) is provided to discharge a gas of a first pressure therethrough, while the second fitting (21B) is provided to discharge a gas of a second pressure therethrough. The first tube (10) has one end to which a first connector (43) connectable to the first fitting (21A) is attached and supplies the first-pressure gas to a first body cavity of a subject. The second tube (22) has one end to which a second connector (44) connectable to the second fitting (21B) is attached and supplies the second-pressure gas to a second body cavity of the subject. The apparatus may comprise an erroneous-connection preventing device (45,RS) preventing an erroneous connection including at
