The present invention provides a ball cock for a railway vehicle which comprises a main body possessing a primary-side opening and a secondary-side opening which face one another and an air exhaust aperture which is formed between these openings. Such ball cock further incudes a ball-shaped valve body which is rotatably provided inside such main body and in which there is formed a communication aperture which connects the primary side opening and the secondary-side opening and a side aperture which, consequent to its rotation, connects the air exhaust aperture and either the primary-side or secondary-side opening. There is formed in the main body's air exhaust aperture a pipe connection to which can be connected a restrictor. In another embodiment an extension pipe is connected to such pipe connection in such air exhaust aperture. Such pipe extension forms a bend portion which causes its opening surface to be positioned lower than a generally horizontal direction when, in accordance with the state in which the main body is fitted to a railway vehicle, its air exhaust aperture is positioned upwardly from such horizontal direction.