A method for determining the adhesion of a foreign matter which is a determining method for determining whether a foreign matter is adhered on an outer surface of a green tire which outer surface is formed by spirally winding a rubber strip, comprising: a raw data acquiring step (Sa) in which an examination surface of the outer surface of the green tire is scanned in the circumferential direction with a two-dimensional displacement sensor, and a raw three-dimensional data of the examination surface is created, an averaging processing step (Sb) in which by averaging processing distance data (z) in the raw three-dimensional data, processed three-dimensional data are obtained, an imaging step (Sc) in which distance data (z) in the processed three-dimensional data are each binarized at a threshold, and an image is created, and a determining step (Sd) in which, based on the data about the created image, whether a foreign matter is adhered is determined, wherein in the raw data acquiring step, the green tire is rotated about its axis, and the two-dimensional displacement sensor irradiates the examination surface of the rotating green tire with a sensor light which is linear and elongate in X direction perpendicular to the circumferential direction, thereby, the raw three-dimensional data made up of position data (x) in the X direction, position data (y) in the circumferential direction, and the distance data (z) from the two-dimensional displacement sensor to the examination surface, are created, and in the averaging processing step, with respect to the raw three-dimensional data D0, for each of the distance data (z), the averaging process is made over a range having a width (Wx) in the X direction and a width (Wy) in the circumferential direction, thereby, processed three-dimensional data are obtained, wherein each of the width wx and the width (Wy) is larger than a spiral pitch of the rubber strip and is smaller than the width of the rubber strip. a raw data acquiring step (Sa) in which an examination surface of the outer surface of the green tire is scanned in the circumferential direction with a two-dimensional displacement sensor, and a raw three-dimensional data of the examination surface is created, an averaging processing step (Sb) in which by averaging processing distance data (z) in the raw three-dimensional data, processed three-dimensional data are obtained, an imaging step (Sc) in which distance data (z) in the processed three-dimensional data are each binarized at a threshold, and an image is created, and a determining step (Sd) in which, based on the data about the created image, whether a foreign matter is adhered is determined, wherein in the raw data acquiring step, the green tire is rotated about its axis, and the two-dimensional displacement sensor irradiates the examination surface of the rotating green tire with a sensor light which is linear and elongate in X direction perpendicular to the circumferential direction, thereby, the raw three-dimensional data made up of position data (x) in the X direction, position data (y) in the circumferential direction, and the distance data (z) from the two-dimensional displacement sensor to the examination surface, are created, and in the averaging processing step, with respect to the raw three-dimensional data D0, for each of the distance data (z), the averaging process is made over a range having a width (Wx) in the X direction and a width (Wy) in the circumferential direction, thereby, processed three-dimensional data are obtained, wherein each of the width wx and the width (Wy) is larger than a spiral pitch of the rubber strip and is smaller than the width of the rubber strip.