A manufacturing method of manufacturing a reinforced electrolyte membrane that is used in a fuel cell and has a reinforcement member disposed inside thereof comprising: a step (a) of conveying a belt-shaped electrolyte polymer that is a belt-shaped body of a first electrolyte polymer in a state disposed on a surface of a first back sheet (1b, 1bB) in a longitudinal direction of the belt-shaped electrolyte polymer as a conveying direction; and a step (b) of conveying a first belt-shaped reinforcement member that is a belt-shaped body in a state disposed on a surface of a second back sheet in the conveying direction and disposing (31, 52, 60) the first belt-shaped reinforcement member on a surface of the belt-shaped electrolyte polymer; characterized by: after the step (b), a step (c) of peeling (33, 54, 61) the first back sheet (1b, 1bB) from the belt-shaped electrolyte polymer in a state where a first adhesiveness between the second back sheet and the first belt-shaped reinforcement member is higher than a second adhesiveness between the first back sheet (1b, 1bB) and the belt-shaped electrolyte polymer; and a step (d) of providing (32, 53, 5) electrolyte polymer (1, 5) between the second back sheet and the first belt-shaped reinforcement member, wherein the step (d) includes before step (c) a step of making the first adhesiveness higher than the second adhesiveness by thermally compressing (32, 53) the belt-shaped electrolyte polymer and the first belt-shaped reinforcement member via the first back sheet and the second back sheet, whereby the first electrolyte polymer that forms the belt-shaped electrolyte polymer is impregnated to the inside of the first belt-shaped reinforcement member and is made to reach an interface between the second back sheet and the first belt-shaped reinforcement member, whereby the first electrolyte polymer provides the electrolyte polymer between the second back sheet and the first belt-shaped reinforcement member. a step (a) of conveying a belt-shaped electrolyte polymer that is a belt-shaped body of a first electrolyte polymer in a state disposed on a surface of a first back sheet (1b, 1bB) in a longitudinal direction of the belt-shaped electrolyte polymer as a conveying direction; and a step (b) of conveying a first belt-shaped reinforcement member that is a belt-shaped body in a state disposed on a surface of a second back sheet in the conveying direction and disposing (31, 52, 60) the first belt-shaped reinforcement member on a surface of the belt-shaped electrolyte polymer; characterized by: after the step (b), a step (c) of peeling (33, 54, 61) the first back sheet (1b, 1bB) from the belt-shaped electrolyte polymer in a state where a first adhesiveness between the second back sheet and the first belt-shaped reinforcement member is higher than a second adhesiveness between the first back sheet (1b, 1bB) and the belt-shaped electrolyte polymer; and a step (d) of providing (32, 53, 5) electrolyte polymer (1, 5) between the second back sheet and the first belt-shaped reinforcement member, wherein the step (d) includes before step (c) a step of making the first adhesiveness higher than the second adhesiveness by thermally compressing (32, 53) the belt-shaped electrolyte polymer and the first belt-shaped reinforcement member via the first back sheet and the second back sheet, whereby the first electrolyte polymer that forms the belt-shaped electrolyte polymer is impregnated to the inside of the first belt-shaped reinforcement member and is made to reach an interface between the second back sheet and the first belt-shaped reinforcement member, whereby the first electrolyte polymer provides the electrolyte polymer between the second back sheet and the first belt-shaped reinforcement member. after the step (b), a step (c) of peeling (33, 54, 61) the first back sheet (1b, 1bB) from the belt-shaped electrolyte polymer in a state where a first adhesiveness between the second back sheet and the first belt-shaped reinforcement member is higher than a second adhesiveness between the first back sheet (1b, 1bB) and the belt-shaped electrolyte polymer; and a step (d) of providing (32, 53, 5) electrolyte polymer (1, 5) between the second back sheet and the first belt-shaped reinforcement member, wherein the step (d) includes before step (c) a step of making the first adhesiveness higher than the second adhesiveness by thermally compressing (32, 53) the belt-shaped electrolyte polymer and the first belt-shaped reinforcement member via the first back sheet and the second back sheet, whereby the first electrolyte polymer that forms the belt-shaped electrolyte polymer is impregnated to the inside of the first belt-shaped reinforcement member and is made to reach an interface between the second back sheet and the first belt-shaped reinforcement member, whereby the first electrolyte polymer provides the electrolyte polymer between the second back sheet and the first belt-shaped reinforcement member.