To provide a flame detector for easily obtaining the angle of visibility matched with the object of fire.

The flame detector 10 is provided with a case body 11 whose one face 11a is provided with an infrared taking-in window 16 and an infrared sensor arranged inside the case body 11 for detecting an infrared ray made incident from the window 16. An ultraviolet sensor 13 is disposed at an infrared sensor setting part 17 provided at the outer peripheral part of the window 16 on one face 11a of the case body 11. The window 16 is provided with a cylindrical housing part with the bottom 16a formed in predetermined width toward the inside part of the case body 11, and an infrared transmitting part 16b formed at the center of the bottom part of the housing part 16a. The housing part 16a of the window 16 can be mounted with a limit adapter piece 15 for applying an infrared ray to an infrared sensor 12 with a predetermined detection angle and detection shape.