b of the outer circumferential surface 12 is extended does not cross with the burr b when the lens 1 is attached to the lens holder of the pickup device the burr does not interfere with the cylindrical surface of the lens holder thus the lens 1 can be accurately positioned to the lens holder here it is preferable that a size of the convex surface 221 d of the metal mold 200 is as small as possible therefore the convex surface 221 d is formed in a neighborhood of the air vent groove 223 and has an arc like shape along the outer circumference forming surface 221 c which is a cylindrical surface further in the embodiment a height d of the convex surface 221 d is set to greater than or equal to 1 5 times of the thickness t see fig1 of the air vent groove 223 for example d 0 03 mm with this configuration a depth of the concaved portion of the lens 1 namely a distance between the virtual cylindrical surface s and the concaved portion 12 a a difference between a radius l 2 at the principal portion 12 b of the outer circumferential surface of the lens 1 and a radius l 3 at the concaved portion 12 a of the lens 1 is substantially equal to the height d of the convex.