In a chemical liquid supplying apparatus 10a for discharging chemical liquid by expanding and contracting a pump chamber 16 which communicates with a chemical liquid inlet 21 and a chemical liquid outlet 22, the apparatus has a cylinder 12 in which a piston 31 is accommodated and reciprocally movable in an axial direction. A bellows 35 which is elastically deformable in the axial direction is mounted to a cylinder hole 30 between the tip of a connection rod 34 and the cylinder 12. On the inside of the bellows 35, an expanding/contracting chamber 37 is formed as a compartment between the connection rod 34 and the bellows 35, a pressure chamber 38 which communicates with the expanding/contracting chamber 37 is provided on the tip side of the piston 31, and an incompressible indirect medium 39 is enclosed in the expanding/contracting chamber 37 and the pressure chamber 38. The average effective diameter D2 of this bellows 35 is set so as to be smaller than the outer diameter D1 of a sliding surface 32 of the piston 31.