A method of mounting a vortex generator to a wind turbine blade, comprising: a step of specifying positions of at least two reference points (P 1,P 2,P 3) at different coordinates in a blade spanwise direction of the wind turbine blade on the wind turbine blade; and a step of adjusting a mounting direction of the vortex generator and mounting the vortex generator to the wind turbine blade, with reference to a line (L ref,L ref1,L ref2) connecting the reference points (P 1,P 2,P 3), wherein the step of specifying the positions of the reference points (P 1,P 2,P 3) comprises specifying the position of each of the reference points (P 1,P 2,P 3) on the basis of a length (l 1,l 1 ') along a surface of the wind turbine blade in a chordwise direction from a trailing edge of the wind turbine blade or from a blade spanwise directional line (Ls) extending along the blade spanwise direction on the surface of the wind turbine blade, and a distance (zl,z2) in the blade spanwise direction from a blade root or from a blade tip of the wind turbine blade, wherein the method further comprises a step of placing a template (30;30A;30B) on the wind turbine blade with reference to the line (L ref,L ref1,L ref2), the template (30;30A;30B) having at least one opening having a shape corresponding to an outline of a platform portion of the vortex generator, wherein the step of mounting the vortex generator comprises fitting the platform portion of the vortex generator into the opening of the template (30;30A;30B) placed on the wind turbine blade and mounting the vortex generator to the wind turbine blade, wherein a mark indicating orientation of the vortex generator including the platform portion to be fitted into the opening is formed on the template (30;30A;30B), wherein the step of mounting the vortex generator comprises adjusting the mounting direction of the vortex generator with reference to the mark of the template (30;30A;30B), while the platform portion of the vortex generator is fitted in the opening, the method being characterized in that the template (30;30A;30B) includes a template body, and a rotary part having the opening and mounted rotatably to the template body, and wherein the method comprises adjusting the mounting direction of the vortex generator by revolving the vortex generator together with the rotary part while the platform portion of the vortex generator is fitted in the opening. a step of specifying positions of at least two reference points (P 1,P 2,P 3) at different coordinates in a blade spanwise direction of the wind turbine blade on the wind turbine blade; and a step of adjusting a mounting direction of the vortex generator and mounting the vortex generator to the wind turbine blade, with reference to a line (L ref,L ref1,L ref2) connecting the reference points (P 1,P 2,P 3), wherein the step of specifying the positions of the reference points (P 1,P 2,P 3) comprises specifying the position of each of the reference points (P 1,P 2,P 3) on the basis of a length (l 1,l 1 ') along a surface of the wind turbine blade in a chordwise direction from a trailing edge of the wind turbine blade or from a blade spanwise directional line (Ls) extending along the blade spanwise direction on the surface of the wind turbine blade, and a distance (zl,z2) in the blade spanwise direction from a blade root or from a blade tip of the wind turbine blade, a length (l 1,l 1 ') along a surface of the wind turbine blade in a chordwise direction from a trailing edge of the wind turbine blade or from a blade spanwise directional line (Ls) extending along the blade spanwise direction on the surface of the wind turbine blade, and a distance (zl,z2) in the blade spanwise direction from a blade root or from a blade tip of the wind turbine blade, wherein the method further comprises a step of placing a template (30;30A;30B) on the wind turbine blade with reference to the line (L ref,L ref1,L ref2), the template (30;30A;30B) having at least one opening having a shape corresponding to an outline of a platform portion of the vortex generator, wherein the step of mounting the vortex generator comprises fitting the platform portion of the vortex generator into the opening of the template (30;30A;30B) placed on the wind turbine blade and mounting the vortex generator to the wind turbine blade, wherein a mark indicating orientation of the vortex generator including the platform portion to be fitted into the opening is formed on the template (30;30A;30B), wherein the step of mounting the vortex generator comprises adjusting the mounting direction of the vortex generator with reference to the mark of the template (30;30A;30B), while the platform portion of the vortex generator is fitted in the opening, the method being characterized in that the template (30;30A;30B) includes a template body, and a rotary part having the opening and mounted rotatably to the template body, and wherein the method comprises adjusting the mounting direction of the vortex generator by revolving the vortex generator together with the rotary part while the platform portion of the vortex generator is fitted in the opening.