A method for manufacturing a vacuum heat insulator (100A-I, 100A-II, 100B-I, 100B-II), the vacuum heat insulator (100A-I, 100A-II, 100B-I, 100B-II) comprising an envelop made by arranging films each having a heat-weld layer and an airtight layer such that the heat-weld layers face each other, and a core member housed in an interior of the envelop , the envelop having a welded part (X1, X2) where the heat-weld layers are heat-welded together in a predetermined width over an entire periphery of the core member and a protective welded part (Y) formed outside the welded part, and the vacuum heat insulator (100A-I, 100A-II, 100B-I, 100B-II) having the interior in an reduced-pressure state, the method comprising the steps of: housing the core member in the interior of the envelop having an unwelded part (X2) where a portion becoming later the welded part is still unwelded; heat-welding the heat-weld layers together under reduced pressure into a state in which all the unwelded part (X2) is welded, after or without heat-welding in advance the heat-weld layers of the unwelded part (X2) while leaving a part thereof necessary for pressure reduction, for the envelop housing the core member , wherein any of the heat-welding is performed to leave outside of the welded part an end part of a predetermined width from an outer edge of the envelop housing the core member ; cleaning surfaces of the heat-weld layers facing each other at the end part of the envelop left outside a post-housing welded part (X2) which has been heat-welded after housing the core member , wherein the cleaning is at least one selected from the group consisting of wiping out a dust on the surfaces using paper or cloth, causing the dust to adhere to a sticky material, blowing away the dust by blowing of air, and sucking the dust by a vacuum cleaner; and forming the protective welded part (Y) to have a region where the cleaned heat-weld layers are heat-welded together outside the post-housing welded part (X2). housing the core member in the interior of the envelop having an unwelded part (X2) where a portion becoming later the welded part is still unwelded; heat-welding the heat-weld layers together under reduced pressure into a state in which all the unwelded part (X2) is welded, after or without heat-welding in advance the heat-weld layers of the unwelded part (X2) while leaving a part thereof necessary for pressure reduction, for the envelop housing the core member , wherein any of the heat-welding is performed to leave outside of the welded part an end part of a predetermined width from an outer edge of the envelop housing the core member ; cleaning surfaces of the heat-weld layers facing each other at the end part of the envelop left outside a post-housing welded part (X2) which has been heat-welded after housing the core member , wherein the cleaning is at least one selected from the group consisting of wiping out a dust on the surfaces using paper or cloth, causing the dust to adhere to a sticky material, blowing away the dust by blowing of air, and sucking the dust by a vacuum cleaner; and forming the protective welded part (Y) to have a region where the cleaned heat-weld layers are heat-welded together outside the post-housing welded part (X2). <EOS>