A flow regulating device comprising: a first housing including a pressure chamber formed therein into which an operating gas is externally introduced; a second housing including a valve chamber formed therein, an upstream flow channel formed therein for providing communication between the valve chamber and an inlet port, and a downstream flow channel formed therein for providing communication between the valve chamber and an outlet port; a valve element part housed in the valve chamber, the valve element part being movable into contact with or away from a valve seat part provided on an inner circumferential surface of the valve chamber so as to form a closed state in which communication is shut off between the upstream flow channel and the downstream flow channel, or an open state in which communication is provided between the upstream flow channel and the downstream flow channel; a diaphragm connected to the valve element part, the diaphragm having a fluid facing surface which faces a fluid, and a gas facing surface which faces the operating gas; a guide member connected to the diaphragm, the guide member that moves with the valve element part in an axial direction of the valve element part in a state in which the guide member is in contact with an inner circumferential surface of the pressure chamber; and a spring that generates a first urging force that causes the valve element part to move in a first direction of the axial direction, a second urging force that causes the guide member to move in a second direction opposite to the first direction is exerted on the guide member when the pressure chamber is pressurized by introducing the operating gas into the pressure chamber, characterized in that the pressure chamber comprises a wide portion and a narrow portion located at a farther position from the valve seat part than the wide portion, and having a smaller width in a diametrical direction perpendicular to the axial direction than the wide portion; wherein the guide member comprises a first guide portion having substantially the same width as the narrow portion, and a second guide portion having a width that is greater than the first guide portion and is substantially the same as the wide portion. a first housing including a pressure chamber formed therein into which an operating gas is externally introduced; a second housing including a valve chamber formed therein, an upstream flow channel formed therein for providing communication between the valve chamber and an inlet port, and a downstream flow channel formed therein for providing communication between the valve chamber and an outlet port; a valve element part housed in the valve chamber, the valve element part being movable into contact with or away from a valve seat part provided on an inner circumferential surface of the valve chamber so as to form a closed state in which communication is shut off between the upstream flow channel and the downstream flow channel, or an open state in which communication is provided between the upstream flow channel and the downstream flow channel; a diaphragm connected to the valve element part, the diaphragm having a fluid facing surface which faces a fluid, and a gas facing surface which faces the operating gas; a guide member connected to the diaphragm, the guide member that moves with the valve element part in an axial direction of the valve element part in a state in which the guide member is in contact with an inner circumferential surface of the pressure chamber; and a spring that generates a first urging force that causes the valve element part to move in a first direction of the axial direction, a second urging force that causes the guide member to move in a second direction opposite to the first direction is exerted on the guide member when the pressure chamber is pressurized by introducing the operating gas into the pressure chamber, characterized in that the pressure chamber comprises a wide portion and a narrow portion located at a farther position from the valve seat part than the wide portion, and having a smaller width in a diametrical direction perpendicular to the axial direction than the wide portion; wherein the guide member comprises a first guide portion having substantially the same width as the narrow portion, and a second guide portion having a width that is greater than the first guide portion and is substantially the same as the wide portion.