Abstract: This invention relates to an electron gun for a color picture tube, comprising a focus electrode structure having three electron beam passage apertures including a center aperture of a circular shape and two side apertures each being of an oblong shape having a major axis extending transversely, being arranged such that the center-to-center distance between adjacent apertures of the three apertures is less than the center-to-center distance between adjacent apertures formed in a control electrode and a screen electrode. This focus electrode structure prevents deterioration of resolution of the picture tube due to changes of electron beam paths resulting from thermal deformation of the electrodes during operation of the gun.