A flow control device comprising: a housing made of resin; a diaphragm which is supported in the housing so as to split the housing into a gas chamber side to which gas is introduced and a fluid chamber side through which fluid passes, and is activated by differential pressure between the gas chamber side and the fluid chamber side; and a valve body which operates in integration with the diaphragm to regulate a flow of the fluid introduced into the fluid chamber side, wherein the flow control device further comprising: a permeation protection sheet which prevents corrosive gas produced from the fluid of the fluid chamber side from flowing into the gas chamber side, the permeation protection sheet being disc-shaped with no center part to match the shape of the diaphragm, wherein the gas chamber side includes a first holding member which holds the diaphragm between itself and an opposing surface of the fluid chamber side opposite to the diaphragm and a cap nut, wherein the first holding member is a support nut, the first holding member is screwed to an inner peripheral wall of the gas chamber side through a screw part, the cap nut is housed on an inner peripheral side of the first holding member, an outer peripheral edge of the diaphragm and an outer peripheral edge of the permeation protection sheet are held between the first holding member and a bottom surface of a first holding member housing part formed on an upper end of the housing, and in inner peripheral edge on a top surface side of the permeation protection sheet is brought into contact with a lower end surface of the cap nut. a housing made of resin; a diaphragm which is supported in the housing so as to split the housing into a gas chamber side to which gas is introduced and a fluid chamber side through which fluid passes, and is activated by differential pressure between the gas chamber side and the fluid chamber side; and a valve body which operates in integration with the diaphragm to regulate a flow of the fluid introduced into the fluid chamber side, wherein the flow control device further comprising: a permeation protection sheet which prevents corrosive gas produced from the fluid of the fluid chamber side from flowing into the gas chamber side, the permeation protection sheet being disc-shaped with no center part to match the shape of the diaphragm, wherein the gas chamber side includes a first holding member which holds the diaphragm between itself and an opposing surface of the fluid chamber side opposite to the diaphragm and a cap nut, wherein the first holding member is a support nut, the first holding member is screwed to an inner peripheral wall of the gas chamber side through a screw part, the cap nut is housed on an inner peripheral side of the first holding member, an outer peripheral edge of the diaphragm and an outer peripheral edge of the permeation protection sheet are held between the first holding member and a bottom surface of a first holding member housing part formed on an upper end of the housing, and in inner peripheral edge on a top surface side of the permeation protection sheet is brought into contact with a lower end surface of the cap nut. a permeation protection sheet which prevents corrosive gas produced from the fluid of the fluid chamber side from flowing into the gas chamber side, the permeation protection sheet being disc-shaped with no center part to match the shape of the diaphragm, wherein the gas chamber side includes a first holding member which holds the diaphragm between itself and an opposing surface of the fluid chamber side opposite to the diaphragm and a cap nut, wherein the first holding member is a support nut, the first holding member is screwed to an inner peripheral wall of the gas chamber side through a screw part, the cap nut is housed on an inner peripheral side of the first holding member, an outer peripheral edge of the diaphragm and an outer peripheral edge of the permeation protection sheet are held between the first holding member and a bottom surface of a first holding member housing part formed on an upper end of the housing, and in inner peripheral edge on a top surface side of the permeation protection sheet is brought into contact with a lower end surface of the cap nut.