To accurately and efficiently form a through hole in a bowl-shaped reflector without hurting a reflecting surface.

A method of boring the reflector includes a process in which the part 34 to be worked of the reflector 3 is arranged between the tips of a pair of outside and inside working core drills 13a and 13b arranged to face each other to move forward/backward on the same axis to cut the bowl-shaped reflector 3 from its outside and inside, a process in which each of the core drills 13a and 13b with the part 34 arranged between their tips is advanced to start the cutting of the part 34 from the inside and outside of the reflector 3, a process in which while the cutting of the part 34 from both sides proceeds to leave a prescribed thickness in the part 34, the outside working core drill 13a is made to retreat from the reflector 3 side, and a process in which after the retreat of the core drill 13a, the inside working core drill 13b is advanced further to form the through hole 33 in the part 34 of the reflector 3.