PURPOSE: To apply simultaneously a chemical on the whole surface of a substrate to be treated and lessen an irregularity in the dimension of a pattern by a method wherein a flat nozzle provided with a multitude of discharge ports is made to approach the substrate or is brought into contact to the substrate to treat the substrate.

CONSTITUTION: A mask 2 which is a substrate to be treated is horizontally placed on a stage 1 in such a way as to oppose to a flat nozzle 3. A chemical tank 4 is pressurized, a valve 5 is opened to discharge a developing solution MIBK through the nozzle 3 and the MIBK is applied on the mask 2 as shown in 6. An arm 12 on the nozzle 6 is coupled with a motor 14 by a coupling 13 and the nozzle 3 is vertically actuated by the rotation of the motor 14. The developing solution is applied through the discharge ports 8. As the MIBK, from which a void 10 is evaporated by making the nozzle 3 approach the MIBK 6 applied on a discharge surface 9 of the nozzle 3, is saturated, vaporization of the MIBK is inhibited and a temperature change is decreased. Accordingly, the evaporation loss of the MIBK is decreased compared with that at the time of the open valve. Thereby, a chemical can be simultaneously applied on the whole surface of the substrate.