PURPOSE: To surely stop a trough part of a wave plate in a welding position of an electrode by inputting a crest/trough signal of the wave plate from a crest/trough detecting sensor and a shaft angle signal of the wave plate and a plate winding shaft from a shaft angle detecting sensor to a controller, and outputting a stop signal to a winding motor, based on both the signals.

CONSTITUTION: A winding shaft 31 of a wave plate 33 and a plate 35 is driven by a winding motor 37. In the upper part of the winding shaft 31, four pieces of wave plate welding electrodes 39 fixed to a welding head 41 are placed, and the welding head 41 is moved in the vertical direction by a motor 43. In the lower part of the winding shaft 31, a plate welding electrode 45 fixed to a welding head 47 is placed, and the welding head 47 is moved in the vertical direction by a motor 49. On the other hand, in the winding shaft 31, a pair of fixed pieces 51 are fixed, and a shaft angle detecting sensor 53 is placed. Also, in the welding head 41, a crest/trough detecting sensor 57 is placed through a bracket 55. A controller 59 inputs a crest/trough signal from the sensor 57 and a shaft angle signal from the sensor 53, outputs a stop signal to the winding motor 37, and stops a trough part of the wave plate 33 in a position of the electrode 39.