An apparatus for coating a polyimide layer includes a printing table in which a substrate is provided, an inkjet head having an injection surface with nozzles for injecting a polyimide liquid onto the substrate, a polyimide liquid supply tank filled with the polyimide liquid, an ultrasonic cleaner in which a cleaning liquid for cleaning the inkjet head is stored for cleaning the inkjet head with vibrations in the cleaning liquid generated by applying an ultrasonic signal, and a wiper for wiping an injection surface of the inkjet head.