To provide an adapter controlling deterioration in appearance a lighting fixture and suppressing swing of the lighting fixture, and to provide a lighting device.SOLUTION: An adapter 10 includes a connector part 70 having a first power feed part 70a electrically connected to a first power feed terminal 123a and a second power feed part 70b electrically connected to a second power feed terminal 123b surrounding the first power feed terminal 123a. The first power feed part 70a includes a first connection terminal 50a electrically connected to the first power feed terminal 123a. The second power feed part 70b is formed so as to surround the periphery of the first connection terminal 50a, and includes a second insertion port part 22b engaged with the second power feed terminal 123b and a second connection terminal 50b electrically connected to the second power feed terminal 123b engaged with the second insertion port part 22b. The second insertion port part 22b includes a projection part 22c abutting on the second power feed terminal 123b so as to support the second power feed terminal 123b.SELECTED DRAWING: Figure 4