To obtain a transformer for lighting a discharge tube in which a switch 28 for stopping protective function can be operated easily and its operator 28p is not damaged easily.

In a transformer case 24, a wiring board 31 mounting an abnormality protective circuit and a circuit for stopping the protective function is disposed in proximity to the case upper plate 24b on the side not fixed with input terminals 14 and 15/output terminals 18 and 19. The wiring board 31 is fixed with a switch 28 oppositely to the upper plate 24b having a hole 41 made oppositely to the switch 28 and the hole 41 is closed by a rubber cap 42. The switch 28 can be operated by pushing the cap 42 from the outside.