A variable flow rate valve mechanism includes a valve, a lock member, a valve attachment member and a spring washer. The valve includes a valve body and a valve shaft. The lock member is fixed to the valve shaft. The valve attachment member is attached to the valve shaft. The spring washer is disposed adjacent the valve attachment member. The spring washer is formed into an annular shape around an axis of the spring washer. The spring washer includes a support portion, a deformable portion and a protrusion portion. The support portion includes a seat surface and an open surface. The deformable portion is connected to the support portion and extends in an inclined manner. The deformable portion includes a contact surface and an opposite surface. The protrusion portion protrudes from at least one of the open surface of the support portion and the opposite surface of the deformable portion.