A method of applying a film to a base material having a bonding surface along a first direction which is an extending direction of the base material, the method comprising the steps of: preparing a film having a main portion extending to the first direction, a first extended portion connected to a first end of the main portion in the first direction, and a second extended portion connected to a second end opposing the first end in the main portion; preparing an application device having a pressing unit including an application unit, a film gripping part that grips the first extended portion of the film, and a second film gripping part that grips the second extended portion of the film, wherein the second gripping part can be driven in a second direction which is a direction orthogonal to the bonding surface; pressing the first extended portion using the pressing unit; applying the main portion to the base material by moving the pressing unit that presses the first extended portion from the first extended portion to the second extended portion via the main portion and by moving the pressing unit in the first and second directions relative to the base material; and stopping the pressing unit moved to the second extended portion and separating the pressing unit from the second extended portion, wherein the first direction is the X-axis direction and the second direction is the Z-axis direction; wherein the angle formed between the X-axis direction and the film prior to pressing is constant while pressing the film with the application unit, and wherein the portion of the film on the opposite site to the side gripped by the film gripping part is gripped in a position where the position in the Z-axis direction is matching with the bonding surface of the base material on the X-axis direction negative which is the opposite side to the side where the base material is provided in the X-axis direction. preparing a film having a main portion extending to the first direction, a first extended portion connected to a first end of the main portion in the first direction, and a second extended portion connected to a second end opposing the first end in the main portion; preparing an application device having a pressing unit including an application unit, a film gripping part that grips the first extended portion of the film, and a second film gripping part that grips the second extended portion of the film, wherein the second gripping part can be driven in a second direction which is a direction orthogonal to the bonding surface; pressing the first extended portion using the pressing unit; applying the main portion to the base material by moving the pressing unit that presses the first extended portion from the first extended portion to the second extended portion via the main portion and by moving the pressing unit in the first and second directions relative to the base material; and stopping the pressing unit moved to the second extended portion and separating the pressing unit from the second extended portion, wherein the first direction is the X-axis direction and the second direction is the Z-axis direction; wherein the angle formed between the X-axis direction and the film prior to pressing is constant while pressing the film with the application unit, and wherein the portion of the film on the opposite site to the side gripped by the film gripping part is gripped in a position where the position in the Z-axis direction is matching with the bonding surface of the base material on the X-axis direction negative which is the opposite side to the side where the base material is provided in the X-axis direction.