Abstract: An outer and inner diameter measuring method for a transparent tube in a non-contact manner includes the steps of irradiating a light having a linear sectional shape, inclined at a pre-determined angle with respect to a plane perpendicular to a length direction of a transparent tube, to the transparent tube; obtaining a light beam pattern formed since the light having a linear sectional shape is intercepted and refracted by the tube; obtaining an inner diameter of the tube by extracting inner diameter information of the tube from the obtained light beam pattern; and obtaining an outer diameter from a light beam pattern refracted by the tube, thereby calculating the outer and inner diameters together.