Process for oversized luggage?

I am a musician and will be travelling to Tokyo. I need to bring two keyboards that have dimensions of 5 ft long 2 ft wide with a 1 ft depth. Each one weighs about 50 lbs each. So is there a special procedure to do this and how can I anticipate the appx costs. Thx.

If you have booked already, give the airline a call, otherwise phone the airlines that serve Japan from the area you are living and take the information into account when deciding what airline to book.