A method for manufacturing a film-wrapped electrical device, comprising: a first injection step of depressurizing, to a given pressure (P A) lower than atmospheric pressure, an inside of an injection chamber in which a bag-shaped laminate film wrapping member is placed, the laminate film wrapping member having an opening portion and housing an electrode assembly including a positive electrode and a negative electrode stacked with a separator therebetween, and injecting part of a predetermined injection amount of an electrolyte solution into the wrapping member through the opening portion; and characterized by a second injection step of, after the first injection step, pressurizing the inside of the injection chamber to a pressure (P B) higher by at least 1kPa than the given pressure (P A) and lower than the half value between the given pressure (P A) and atmospheric pressure, by introducing a gas into the injection chamber through a gas introduction line connected to the injection chamber, and injecting the rest of the predetermined injection amount of the electrolyte solution, in each of the first injection step and the second injection step, the solution is injected in installments, a total injection amount in the first injection step is set larger than a total injection amount in the second injection step, a number of times of installments in the first injection step is set larger than a number of times of installments in the second injection step, the total injection amount in the first injection step is divided and an injection amount in each installment in the first injection step is set such that a sum of the injection amount in each installment in the first injection step becomes the total injection amount in the first injection step, and the total injection amount in the second injection step is divided and an injection amount in each installment in the second injection step is set such that a sum of the injection amount in each installment in the second injection step becomes the total injection amount in the second injection step, in the first injection step, the inside of the injection chamber is kept at the given pressure (P A) after the depressurizing, and in the second injection step, the inside of the injection chamber is kept at the pressure (P B) after pressurizing. a first injection step of depressurizing, to a given pressure (P A) lower than atmospheric pressure, an inside of an injection chamber in which a bag-shaped laminate film wrapping member is placed, the laminate film wrapping member having an opening portion and housing an electrode assembly including a positive electrode and a negative electrode stacked with a separator therebetween, and injecting part of a predetermined injection amount of an electrolyte solution into the wrapping member through the opening portion; and characterized by a second injection step of, after the first injection step, pressurizing the inside of the injection chamber to a pressure (P B) higher by at least 1kPa than the given pressure (P A) and lower than the half value between the given pressure (P A) and atmospheric pressure, by introducing a gas into the injection chamber through a gas introduction line connected to the injection chamber, and injecting the rest of the predetermined injection amount of the electrolyte solution, in each of the first injection step and the second injection step, the solution is injected in installments, a total injection amount in the first injection step is set larger than a total injection amount in the second injection step, a number of times of installments in the first injection step is set larger than a number of times of installments in the second injection step, the total injection amount in the first injection step is divided and an injection amount in each installment in the first injection step is set such that a sum of the injection amount in each installment in the first injection step becomes the total injection amount in the first injection step, and the total injection amount in the second injection step is divided and an injection amount in each installment in the second injection step is set such that a sum of the injection amount in each installment in the second injection step becomes the total injection amount in the second injection step, in the first injection step, the inside of the injection chamber is kept at the given pressure (P A) after the depressurizing, and in the second injection step, the inside of the injection chamber is kept at the pressure (P B) after pressurizing.