A color cathode ray tube apparatus having an electron gun assembly including a device for modulating a scanning velocity of electron beams at an auxiliary lens section for clarifying an image projected to a screen is disclosed. The color cathode ray tube apparatus comprises an enclosure having a panel section, a funnel section and a neck section, an electron gun assembly, including rear electrodes disposed in front of three cathodes for emitting electron beams, each having three through-holes for passing the beams for forming an auxiliary lens for preliminarily focusing the beams, and a front electrode located in front of the rear electrodes for forming a main lens in cooperation with one electrode thereof for further focusing the beams and converging the beams. The rear electrodes have a pair of electrode members having three beam through-holes defined by cylindrical projections, oblique surfaces opposed at a predetermined interval, formed of the cylindrical projections, each surface crossing perpendicularly to a horizontal plane for scanning the beams and having a predetermined angle with respect to a plane perpendicular to the axis of an electron beam path. The scanning velocity modulating device is connected with the pair of electrode members for supplying a modulating voltage thereto, when luminance values of a video signal arrive at a predetermined level.