To provide a fluorescent lamp with improved characteristics such as efficiency by optimizing temperature at the coldest point.

If the major diameter of a straight tube 9 is d, and that of a bending part 8 is D, 0.8≤D<d. Height in longitudinal direction of a luminous tube 5 can be suppressed, height in longitudinal direction of the fluorescent lamp can be suppressed, and so, more compact size is attained. Even if the height is low, length of a discharge path can be secured, making its efficiency improved. Even with a small-sized fluorescent lamp with an input power toward it of 12W or less, temperature of the coldest point can be set at a given temperature. Degradation of efficiency can be prevented even if the temperature of the coldest point is low. If the major diameter at a corner part of the bending part 8 is Dd, the temperature of the bending part 8 which normally is the coldest point can be set appropriately with: 1.2d≤Dd≤1.5d. Mercury vapor pressure can be prevented from rising higher than necessary.