A cathode ray tube includes a panel having a substantially flat outer surface and an inner curved surface with a phosphor screen. The panel has a substantially rectangular effective screen portion with two long sides parallel to each other, two short sides parallel to each other and four rounded edges interconnecting each long side and the neighboring short side. The effective screen portion is structure such that a first line V1 interconnecting centers of the long sides, a second line H1 interconnecting centers of the short sides and a third line D1 interconnecting centers of the rounded edges opposite to each other meet at a point. The effective screen portion has a first thickness Tv at the centers of the long sides, a second thickness Th at the centers of the short sides, a third thickness Td at the centers of the edges and a fourth thickness Tc at the meeting point of the all three lines V1, H1 and D1. A shadow mask is disposed within the panel so that the shadow mask faces the inner curved surface of the panel. The shadow mask has a curvature corresponding to the inner curved surface of the panel. The ratio of the second thickness Th to the third thickness Td while subtracting the fourth thickness Tc from each thickness satisfies the following condition: 0.75(Th-Tc)/Td-Tc).ltoreq.0.85, and the ratio of the first thickness Tv to the thickness Td while subtracting the fourth thickness Tc from each thickness satisfies the following condition: 0.75.ltoreq.(Tv-Tc)/(Td-Tc).ltoreq.0.85.