A photo mask formed with patterns to be transferred to a substrate using an exposure apparatus, the photo mask comprising a pattern row having three or more hole patterns surrounded by a shielding portion or a semitransparent film and arranged along one direction, and an assist pattern surrounded by the shielding portion or semitransparent film and having a longitudinal direction and a latitudinal direction, the assist pattern being located at a specified distance from the pattern row in a direction orthogonal to the one direction, the longitudinal direction of the assist pattern being substantially parallel with the one direction, the longitudinal length of the assist pattern being equivalent to or larger than the longitudinal length of the pattern row, the assist pattern being not transferred to the substrate.