A drill for forming through holes in a glass fiber reinforced substrate includes a drill body having a cutting edge part on a front end side, and a neck part on a base end side. The cutting edge part has a larger diameter than the neck part. The drill body has a step formed between the cutting edge and neck parts and a single continuous chip evacuation groove having main and secondary grooves. The main groove has an L-shaped cross section and is extending from front end of the cutting edge part over the step to the neck part. The secondary groove has a U-shaped cross section and smaller groove width and depth than the main groove and is extending along the main groove from the front end of the cutting edge part over the step to the neck part and merging into the main groove at the neck part.