To provide a construction method of a launching slipway capable of shortening a construction time and enhancing construction accuracy of the launching slipway and a rail, and easy to maintain and control, when constructing the launching slipway sticking into the water from the land.

A launching slipway tip part 13 having a rail 4a laid on a float 14 and a slipway 15 above the float is constructed on the land area A. The launching slipway tip part 13 is tugged to the tip water area C of a launching slipway land part 23. It is then seated on the bottom 21 of the water at the launching slipway tip part by filling ballast on the float 14 of the launching slipway tip part.