To easily change a desired fluorescent lamp by installing joining tools to be installed through instruction grooves formed in the tip end parts of main bodies and a connecting tool to connect the joining tools one another.

When main bodies 1 are fixed at positions where the main bodies are to be fixed by fastening tools such as screws through fixing holes 72 formed in fixing pieces 70 and then the main bodies 1 are pushed to the fixing piece 70 side, the main bodies 1 are fixed by elastic doublewing pieces of the U-shaped fixing pieces 70. A long grooves 31 is formed in the upper face of the cover 30 in the longitudinal direction and the main bodies 1 are joined through joining tools 40 to be fitted in the tip end parts of the main bodies and a connection tool 50 to connect these joining tools 40. The connection tool 50 to join the joining tools 40 one another has a box-like shape and partitioning wall 51 in the center and joining pieces 52 are installed in the inside part. Consequently, an power source between the main bodies 1 is shut off by pulling out the connection tool 50 and the main body 1 out of order can be changed while the connection tool 50 being taken out.