To reduce the influence of heat or the like on a substrate in the manufacture of an electron emission element by varying the irradiation position of a laser beam for each of the first and second machining processes and machining the same line.

A sample 16 is set in an XY direction scanning mechanism 15, and the output of a laser oscillator 11 is set in the desirable value with a control computer 18. A control signal is sent to a position control mechanism 17 from the mechanism 15 so that the mechanism 15 moves according to a machining pattern, and the mechanism 15 is driven. At that time, a pulse laser beam is irradiated from the oscillator 11. This process is repeated to form a desirable trimming pattern. When machining is performed by using the laser beam of the illustrated output wave form, in a first machining, the wave form having machining pitch L1 and power Pw1 is used, and in a second machining, the wave form having machining pitch L2 and power Pw2 is used. Two wave forms are shifted by Lα. By shifting the wave forms and performing machining plural times, the total energy applied to the substrate can be reduced.