To provide an exposed type fluorescent luminaire for ceiling using a so-called T8 type 110 W straight pipe fluorescent lamp 13 that hardly falls and is not mistakenly changed for a T12 type 110 W straight pipe fluorescent lamp.

This luminaire comprises a luminaire body 10 to be arranged at a high place. A pair of lamp sockets 12 facing each other is mounted on a bottom face of a luminaire body 10. A straight type fluorescent lamp 13 is horizontally arranged along the bottom face of the luminaire body 10 and detachably mounted between the pair of lamp sockets 12. The straight type fluorescent lamp 13 is 25.0-26.0 mm in its tube outside diameter and 2300-2400 mm is its length, and is of an exposed type such that a light transmission cover covering the straight type fluorescent lamp 13 from below is not mounted thereto and the lamp 13 is exposed in its lower side. An auxiliary lamp holder 14 is mounted on the bottom face side of the luminaire body 10 at an intermediate position of the pair of a lamp sockets 12. A form of the auxiliary lamp holder 14 is determined so that the straight type fluorescent lamp 13 is detachably held and a fluorescent lamp with a tube outside diameter of about 38 mm can not be held.