A wet treatment method of a metal-ceramic bonded member of a base integral type which is so structured that a metal-ceramic bonded member is bonded on a base member (11, 11'), the metal-ceramic bonded member being constituted of a ceramic substrate and a circuit pattern forming metal plate bonded on the ceramic substrate, the method comprising: having a masking member cover said metal-ceramic bonded member of the base integral type, wherein said masking member comprises a window portion from which the ceramic substrate is exposed and the base member (11, 11'), that is bonded on the ceramic substrate, is exposed in a portion surrounding the ceramic substrate; pressing said masking member against said exposed base member so as to prevent a treatment solution for said wet treatment from passing through a portion where said masking member and the base member exposed in the portion surrounding said ceramic substrate are in contact with each other; and during pressing said masking member, bringing the treatment solution for the wet treatment of said circuit pattern forming metal plate into contact with said circuit pattern forming metal plate wherein the masking member comprises a base having said window portion; a pressing portion (63, 64) having a further window portion that has the same size and the same position as said window portion and is suitable to be deformed by a pressing force; and a plurality of elastic members, wherein said pressing portion (63, 64) is disposed on said base via said plural elastic members, wherein said masking member accommodates said metal-ceramic bonded member of the base integral type such that the circuit pattern forming metal plate side of the bonded member of a base integral type accommodated in the masking member is exposed via the window portions; wherein said base member (11, 11') is pressed against said pressing portion (63, 64); and wherein pressing the bonded member of a base integral type against the masking member comprises pressing a back board against the back of the base member (11, 11') and fastening the back board and the masking member with fastening tools in order to press the bonded member of a base integral type against the masking member. having a masking member cover said metal-ceramic bonded member of the base integral type, wherein said masking member comprises a window portion from which the ceramic substrate is exposed and the base member (11, 11'), that is bonded on the ceramic substrate, is exposed in a portion surrounding the ceramic substrate; pressing said masking member against said exposed base member so as to prevent a treatment solution for said wet treatment from passing through a portion where said masking member and the base member exposed in the portion surrounding said ceramic substrate are in contact with each other; and during pressing said masking member, bringing the treatment solution for the wet treatment of said circuit pattern forming metal plate into contact with said circuit pattern forming metal plate wherein the masking member comprises a base having said window portion; a pressing portion (63, 64) having a further window portion that has the same size and the same position as said window portion and is suitable to be deformed by a pressing force; and a plurality of elastic members, wherein said pressing portion (63, 64) is disposed on said base via said plural elastic members, wherein said masking member accommodates said metal-ceramic bonded member of the base integral type such that the circuit pattern forming metal plate side of the bonded member of a base integral type accommodated in the masking member is exposed via the window portions; wherein said base member (11, 11') is pressed against said pressing portion (63, 64); and wherein pressing the bonded member of a base integral type against the masking member comprises pressing a back board against the back of the base member (11, 11') and fastening the back board and the masking member with fastening tools in order to press the bonded member of a base integral type against the masking member.