To provide a base for a circular lamp adaptable to a conventional lamp socket and capable of restraining generation of tracking as well as a circular fluorescent lamp with the base.

The base for a circular lamp 15 is provided with a first concave part 16 formed on an outer face of a base member 2 between a first and a second connection pins 4, 4, a second concave part 17 formed nearly at a middle part of one of the base members 2 between the connection pins 4, equipped with an insertion hole 19 on a bottom face 17b into which a screw 18 is inserted from a connection pin 4 side, and having a depth deep enough for a head part 18a of the screw 18 to be positioned further inward into the base member 2 than a bottom face 16b of the first concave part 16 when the screw 18 is inserted into the insertion hole 19, and the screw 18 jointing the pair of base members 2, 3.