A constant flow control device that controls a flow rate of fluid at a predetermined flow rate comprising: a diaphragm, a first chamber that is formed by a first housing including an inlet into which fluid flows from an upstream fluid passage, and by a movable valve body integrally attached to the diaphragm, wherein an upper part of the movable valve body is opposed to the first housing, a second chamber that is formed by a second housing including an outlet communicating with a downstream fluid passage, and by the movable valve body, wherein the lower part of the movable valve body is opposed to the second housing; a throttle portion configured to communicate the first chamber with the second chamber and pass fluid in order to cause a difference of pressures between the first chamber and the second chamber; a valve seat provided in such a way as to face a passage communicating the second chamber with the downstream fluid passage, and provided in such a way as to correspond to a needle valve included in the movable valve body; and a main elastic member configured to bias the movable valve body in a direction in which the needle valve and the valve seat open by a predetermined elastic force characterized in that, wherein the needle valve is held at the movable valve body in such a way as to move forward and backward in a same direction as a direction in which the movable valve body can move, and a motion of the needle valve in a direction toward the valve seat is limited at a predetermined position of the movable valve body, the throttle portion is provided at the movable valve body, a needle valve elastic member provided at the movable valve body biases the needle valve in a direction toward the valve seat, when a differential pressure between the first chamber and the second chamber exceeds a predetermined differential pressure prescribed by a biasing force of the main elastic member, the movable valve body can move to a movable valve body receiving portion included in the second housing in the direction toward the valve seat and is received by the movable valve body receiving portion while the needle valve is closely contacted with and touches down on the valve seat, such that the movable valve body receiving portion receives a force of an excess in the differential pressure, the throttle portion is formed such that a component separate from a body of the movable valve body is incorporated in the body of the movable valve body, a concave portion communicated with the second chamber is provided at the movable valve body, a base end side shaft of the needle valve is slidably incorporated in a bottom of the concave portion provided at the movable valve body, and an end opposite to the needle valve of the needle valve elastic member is received by the throttle portion integrally fixed to a first chamber side of the concave portion of the movable valve body. a diaphragm, a first chamber that is formed by a first housing including an inlet into which fluid flows from an upstream fluid passage, and by a movable valve body integrally attached to the diaphragm, wherein an upper part of the movable valve body is opposed to the first housing, a second chamber that is formed by a second housing including an outlet communicating with a downstream fluid passage, and by the movable valve body, wherein the lower part of the movable valve body is opposed to the second housing; a throttle portion configured to communicate the first chamber with the second chamber and pass fluid in order to cause a difference of pressures between the first chamber and the second chamber; a valve seat provided in such a way as to face a passage communicating the second chamber with the downstream fluid passage, and provided in such a way as to correspond to a needle valve included in the movable valve body; and a main elastic member configured to bias the movable valve body in a direction in which the needle valve and the valve seat open by a predetermined elastic force characterized in that, wherein the needle valve is held at the movable valve body in such a way as to move forward and backward in a same direction as a direction in which the movable valve body can move, and a motion of the needle valve in a direction toward the valve seat is limited at a predetermined position of the movable valve body, the throttle portion is provided at the movable valve body, a needle valve elastic member provided at the movable valve body biases the needle valve in a direction toward the valve seat, when a differential pressure between the first chamber and the second chamber exceeds a predetermined differential pressure prescribed by a biasing force of the main elastic member, the movable valve body can move to a movable valve body receiving portion included in the second housing in the direction toward the valve seat and is received by the movable valve body receiving portion while the needle valve is closely contacted with and touches down on the valve seat, such that the movable valve body receiving portion receives a force of an excess in the differential pressure, the throttle portion is formed such that a component separate from a body of the movable valve body is incorporated in the body of the movable valve body, a concave portion communicated with the second chamber is provided at the movable valve body, a base end side shaft of the needle valve is slidably incorporated in a bottom of the concave portion provided at the movable valve body, and an end opposite to the needle valve of the needle valve elastic member is received by the throttle portion integrally fixed to a first chamber side of the concave portion of the movable valve body.