The relation between the Muller-Lyer illusion and the angle illusion was investigated experimentally. Fifteen university students estimated the apparent angles of the oblique lines and the apparent lengths of the shaft lines of the Muller-Lyer figures. In the case of the in-going Muller-Lyer figure, the angles of the oblique lines were overestimated and the lengths of the shaft lines were underestimated. In the case of the out-going Muller-Lyer figure, the angles of the oblique lines were underestimated and the lengths of the shaft lines were overestimated. It was found that the negative correlation coefficient between the angle illusion magnitudes and the Muller-Lyer illusion magnitudes was significant.