PURPOSE: To regulate the inner pressure of the sarcocarp discharge part of a screw type fruit juice finishing machine.

CONSTITUTION: A plug 32 which is mounted on a pneumatic cylinder 34 through a metal clamper 38 supported at a U-shaped stepped cavity and has a sealing surface whose outside diameter is next to the inside diameter 42 of a plug housing 44 is fitted at a discharge valve 26 formed on a fruit juice finishing machine. The plug 32 is disposed against sarcocarp 28 by the pneumatic cylinder so as to seal a window 52. When the pressure the sarcocarp acts on the plug exceeds opposing pressure applied by the pneumatic cylinder, the plug is pushed back, so that the sarcocarp passes through the window and is discharged from a sarcocarp outlet chamber 36.