The Four-lanes widening construction in WAKATO bridge is to change RC slab for steel deck with assuring the regular traffic to run. Some problem about it were studied before this work technically or constitutively. We should reported here of an observation result and management of deformation caused by the variation of load system. In the meantime, the variation of vibration characteristics, the affection to stability of active and wind-standing with the construction are also dealt with. The

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... ult was that it is a best method for deformation management to use a water-level connecting pipe that made the measurement data in accordance with the calculation almost. Therefore, the method and procedure of construction this time may be thought adoptable. On the other hand, the vibration characteristics has no any difference with widening. Stability of the widened bridge with wind-standing equipment is better than it was.