A sensor head has a multiplicity of linear image sensors in correspondence with different radial directions of light emitted from a pixel in a pixel line of an LCD panel. The linear image sensors extends in the direction of the axis of an imaginary semi-cylinder. The linear image sensors have light receiving faces that are angularly spaced apart on an imaginary semi-cylinder, with their light receiving faces having normals passing through the axis of the imaginary semi-cylinder. Interposed in the space between the LCD pixel and the linear image sensors is an optical system having a multiplicity of light paths associated with respective angular components of the radiation emitted from the pixel line. Each of the light paths receives a predetermined angular component of light and transmits the light thus reveived to a corresponding one of the linear image sensors.