A slit coater including an apparatus for supplying coating solution by a coating method using a slit nozzle, which is configured to minimize contamination of coating solution, utilizing a filtering function, and supplying a controlled amount of photosensitive solution to a slit nozzle. The slit coater further includes a table on which an object to be processed is mounted, a slit nozzle unit that applies coating solution onto a surface of the object to be processed, and a coating solution supply apparatus including a storage tank that stores the coating solution, a pump that supplies the coating solution stored in the storage tank to the slit nozzle unit, and a buffer tank that is in fluid communication with the pump and the storage tank.