To provide a control valve system having both of an excellent constant flow control function and a liquid level control function by a small float, to automatically carry out control of a flow rate and a liquid level and hard to cause hunting etc.

A flow control valve 6 to set a flow valve and a sliding valve 7 to carry out automatic throttle control work are serially provided, a sliding valve 7 is fitted on a bulkhead member 4 in a valve chest 1 tightly sealed and free to slide, an energizing means 8 to constantly energize a sliding valve opening (d) in a direction to open by specified force is installed, a bag chamber (f) broadly formed on the opposite side of an intermediate chamber (c) by sandwiching the sliding valve 7 is communicated to an inlet channel (a), an automatic throttle control channel is constituted on the sliding valve opening (d), the flow control valve 6 is connected to a float 31 and constituted to automatically close it when its float liquid level reaches the upper limit, the flow control valve 6 is connected to a flow control valve oscillation restraining device 11 and it is constituted in structure to restrain oscillation of the flow control valve 6.