PURPOSE: To make it possible to easily replace a fluorescent lamp only by detaching a fixing device by connecting a pair of air flow boards, left and right, to each other by means of the fixing device and detachably mounting a holding member fixed to the fixing device to the fluorescent light to hold the air flow boards with respect to said light.

CONSTITUTION: In a plurality of air flow boards 51, 52, legs 88, 89 formed at the lower edge of each of the boards are positioned on a bottom plate in front and in rear of a plurality of cold air delivery ports. The rear parts of the boards 51, 52 are secured to a rear fixing device 91 through screws 92 and the upper parts thereof are fixed to the device 91 through an upper fixing device 93. In this case, a front fixing device 96, as a fixing device, is fixed to the front parts of the boards 51, 52 and a clip 97, as a holding member, is engaged with an engaging hole 96D. And a holding part 97B of the clip 97 is detachably mounted to a fluorescent lamp 74. As a result, the boards 51, 52 are held with respect to the lamp 74 and by detaching the device 96 only, the light 74 can be easily replaced.