NOVELTY - The device has a substrate holding portion for holding a substrate (W) in a horizontal posture. A rotating portion rotates the substrate held in the holding portion. A heating portion injects heating steam (51) into an upper surface peripheral edge part (S3) of the substrate. A gas injecting head portion injects gas from the substrate into a predetermined injection target region defined within a range surrounded by a rotating track of the edge part in an upper surface (S1) of the substrate to generate a gas flow, which flows from the region toward the edge part on the substrate.    USE - Substrate processing device for carrying out chemical treatment i.e. etching, while rotating a substrate. Uses include but are not limited to a semiconductor wafer, optical disk substrate, magnetic disk substrate, magneto-optical disk substrate, photomask substrate and a solar cell substrate.    ADVANTAGE - The device prevents mist obtained by condensation of the steam and mist-like processing liquid from adhering onto a non-processed region of the upper surface of the substrate, thus supplying a sufficient amount of steam for heating the peripheral edge part of the substrate, while suppressing deterioration in the non-processed region due to the adhering of the mist. The device carries out the chemical treatment for the peripheral edge part and the lower surface in the substrate, while suppressing a drop in temperature of the peripheral edge part of the substrate to reduce energy required for heating the peripheral edge part, thus suppressing wraparound of the processing liquid from the lower surface of the substrate to the peripheral edge part of the upper surface of the substrate by reducing rotating speed of the substrate and controlling processing width of the peripheral edge part in an easy manner. The device supplies the processing liquid from a processing liquid discharging portion to the upper surface peripheral edge part portion heated by the steam injecting portion immediately after heating, so that etching is carried out for the portions of the upper surface peripheral edge part heated by the steam injecting portion when the temperature is prevented from being reduced, thus enhancing etching rate, preventing temperature of the peripheral edge part of the substrate from being reduced and reducing change in chemical activity of the processing liquid, and hence suppressing consumption of the processing liquid and time required for the processing.    DETAILED DESCRIPTION - The heating portion is a steam injecting portion (121). The steam is superheated steam. An INDEPENDENT CLAIM is also included for a substrate processing method for carrying out chemical treatment for a substrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a side view of a nozzle unit structure.    Upper surface of substrate (S1)    Upper surface peripheral edge part (S3)    Substrate (W)    Heating steam (51)    Nozzle unit (120)    Steam injecting portion (121)    Processing liquid discharging portion (122)    Nozzles (125-127)    Rigid tubular piping arm (180)    Pipes (181-183)