To provide a constant flow rate valve capable of reducing noise generated when controlling a flow rate of wastewater substantially constant.

The constant flow rate valve 33 controlling the flow rate of the wastewater W5 flowing through a wastewater line L51 substantially constant by passing the wastewater W5 flowing through the wastewater line from a primary side 33A to a secondary side 33B has a cylindrical constant flow rate valve body 331 in which the waste water passes, an orifice 332 having a plurality of hole parts 334a arranged in the primary side 33A of the constant flow rate valve body 331, a cylindrical noise eliminating ring 335 arranged in the secondary side 33B of the constant flow rate valve body 331, the noise eliminating ring 335 is formed in the primary side 33A of the noise eliminating ring 335 such that the diameter becomes smaller from the primary side 33A to the secondary side 33B of the constant flow rate valve 33 and has an entrance side inner peripheral surface part 335a with which at least a part of the wastewater having passed through the plurality of hole parts 334a collides.