A method for manufacturing a photomask includes forming a photoresist film on a substrate, and forming a defect detecting pattern on the photoresist film. The defect detecting pattern has a first pattern elongated in a first direction and a second pattern overlapping one end of the first pattern and elongated in a second direction different from the first direction. The first pattern and the second pattern are formed using electron beams (e-beam) diffracted by a same amplifier.