Abstract: Disclosed is a ceiling recessed-type lamp unit, which is capable of facilitating recessedly mounting a unit body to a ceiling, in a reliable manner regardless of a lamp unit's size. The lamp unit comprises a support member 3, and an engagement member 4. The support member 3 is formed with a latch portion adapted to engage the engagement member 4, and a guide groove successively extending from the latch portion downwardly. The engagement member 4 is formed with a first engagement portion 4a engageable with the latch portion, and a second engagement portion 4b engageable with a back surface of a ceiling T. The engagement member 4 is adapted to be rotated in a first direction about a vertical axis thereof, so that the first engagement portion 4a is latchedly engaged with the latch portion to allow the engagement member 4 to be set in a non-engagement position where the second engagement portion 4b avoids engagement with the back surface of the ceiling T.