To simply and highly-accurately execute work for drilling a second bolt hole in a second plate material so as to be located coaxially with the first bolt hole of a first plate material after overlapping the first/second plate materials on each other.

A drill guide jig J2 is used for drilling a second bolt hole 13d, coaxial with a first bolt hole 12b of an outer panel 12, in an access panel 13 after overlapping the access panel 13 on the rear face of the outer panel 12. The jig includes: a cylindrical jib body 31 that allows a drill D to penetrate therethrough; a tapered part 32 formed at one end of the jig body 31; and a flange 33 formed on the outer periphery of the jig body 31. The tapered part 32 is fitted to the tapered opening 12c of the first bolt hole 12b. The drill D is penetrated through the cylindrical jig body 31 while the flange 33 is brought into contact with the periphery of the opening 12c. Consequently, the second bolt hole 13d is highly-accurately machined in the access panel 13 without displacement or an inclination.