The blocker described comprises: a lens illumination light source; a light transmission and reflection device to reflect/transmit the light; an image sensor to detect light reflected by the light transmission and reflection device and thereby obtain an lens image; a lens meter to detect the light that has passed through the light transmission and reflection device to thereby measure lens characteristics; and a blocking member to attach a leap block to the lens. The light transmission and reflection device comprises: a first reflection plate having a central hole; a first rotating cylinder to be coupled to and to rotate the first reflection plate; a second rotating cylinder located inside and to rotate the first rotating cylinder; a second reflection plate, adjusted by the second rotating cylinder and configured to open or block the central hole in the first reflection plate; and driving means configured to drive the second rotating cylinder.