PURPOSE: To effectively form an etching resist layer by a simple work by dipping an entire board in photosensitive resist liquid in a step of forming the resist layer, and deaerating bubbles in hole for a through hole.

CONSTITUTION: A hole 10 for a through hole is opened at an insulating board 1, a conductor metal layer 2 is formed by a plating method, and then dipped in photosensitive resist liquid 3 of a storage tank 4 in which viscosity, thixotropy value, etc., are regulated. When the tank 4 is introduced into a pressure reducing chamber 5 and reduced under pressure, bubbles B in the hole 10 are floated to be removed. When the board 1 in which the liquid 3 is adhered is lifted, after deaerated, and dried, the board 1 covered with an etching resist layer 30 is obtained. Since the fluidity of the liquid 3 is low, the layer 30 is connected to become a joint 31, but it does not affect an influence to its function. It is exposed with an ultraviolet ray by using a mask pattern, developed, the layer 30 of an unnecessary part is removed to form the layer 30 of a predetermined pattern.