Thermal electron energy distributions in the midlatitude ionosphere measured at dusk on September 16, 1983, by a Japanese rocket S-310-14, launched from Kagoshima Space Center, showed bumps appeared on the high energy tail at about 0.3eV between 98.3 and 171km. Densities of such non-thermal electrons were about 10-2 of those of thermal electrons. Above the height of 180km (F-layer), distributions had no bumps on the tail and only slightly deviated from Maxwellian. The mechanism of the appearance of non-thermal electrons is discussed from a point of super-elastic collisions between vibrationally excited nitrogen molecules and thermal electrons.