An insulating film is formed on a main surface of a substrate. A conductive film is formed on the insulating film. A lower layer resist film, an intermediate layer, an anti-reflection film and an upper layer resist film are formed on the conductive film. A focal point at a time of exposure is detected by detecting a height of the upper layer resist film. In detecting the focal point at the time of exposure, a focal point detection light is radiated on the upper layer resist film. After detecting the focal point, the upper layer resist film is exposed and developed thereby to form a resist pattern. With the resist pattern as a mask, the intermediate layer and the anti-reflection film are patterned, and the lower layer resist film is developed. With these patterns as a mask, the conductive film is etched thereby to form a gate electrode.