An apparatus for measuring spherical aberrations of photographic lenses is described. Instead of photographic plates, a solid state linear image sensor is successfully applied to give an increased accuracy, because it allows us to analyze the intensity distributions of the pinhole images. A drastic improvement is also obtained in the measuring efficiency by using an online computer directly connected with the image sensor. It is shown that some changes should be made in the measuring procedure in order to apply a solid state image sensor to Hartmann Test. Two standard lenses of known data are measured to test the apparatus. Then the limitations and the precision of the method are discussed in both theoretical and experimental manners.