PURPOSE: To enhance the manufacturing efficiency of a hollow yarn like separation membrane by containing a wetting agent with moisture content of 15% or less in the hollow yarn like separation membrane and uniformizing the moisture distributions of the outer and inner peripheral parts thereof to form a hollow yarn like separation membrane bundle.

CONSTITUTION: A hollow yarn membrane is immersed in an aqueous solution containing a wetting agent to diffuse the wetting agent in the pore parts of the hollow yarn membrane to adhere the same to the pores thereof. Next, a predetermined number of hollow yarn membranes having the wetting agent adhered thereto and having an inner diameter of 0.10-1.8mm are cut into a definite length to form a yarn bundle. When a high frequency wave is applied to the hollow yarn membrane bundle, the selective dielectric heating of water is generated because the dielectric constant of water is especially high. The frequency of the high frequency wave to be used is pref. 1-20MHz and more pref. 10-15MHz. The obtained hollow yarn membrane bundle is a wet one with moisture content of 15% or less and the moisture content in the bundle can be made uniform in a short time.