To provide a flow controller capable of carrying out an adjustment of a flow rate of a fluid.

The flow controller 1 has a cylindrical body 2; a flow passage control member 4; an operation member 7; and a support 9. The cylindrical body 2 is provided with a deformable part 12, the flow passage control member 4 is provided with a control groove 15 and the operation member 7 is provided with an urging part 6. The flow passage control member 4 has a loose circular curved surface 10 near a border 20 at a flow passage side of the cylindrical body 2 and the flow passage control member 4. When the deformable part 12 is urged by the urging part 6, a gap is hardly generated by making the cylindrical body 2 and the flow passage control member 4 coincident with each other except for an adjustment flow passage. When an inner periphery length of the cylindrical body 2 is set to a shorter length than a periphery length of a cross section of the flow passage control member except for a control groove, a gap is not further generated.