PURPOSE: To obtain the bulb for a projection picture tube which has a relatively small size in an external shape and a relatively large size in an effective screen by providing a reinforcing structure which is loosely slanted in the inner surface of a panel skirt and is thickened in the thickness of the base portion of the panel skirt along only the long side of the effective screen.

CONSTITUTION: The inner surface of a panel skirt portion is slanted at 18° against the perpendicular line of a panel surface to fairly thicken the base portion of the skirt portion in the section of line A-A' along the long side of an effective screen. On the other hand, the inner surface of the panel skirt portion is slanted at only 3° against the perpendicular line of the panel surface in the section of line B-B', and the thickness of the base portion of the skirt portion is not thickened. Whereby, it is possible to reduce the length in a horizontal direction in the external shape 7b of a panel in comparison with the size of the effective screen 8b and further to obtain desired strength which can withstand the pressure rising of refrigerant. The advantage of reduction of the length in a horizontal direction is large, and in the case of the ratio of 4 broad and 3 long in the shape of the effective screen, the external shape of the panel is longer more and less in the length than in the breadth. As a result, when projection cathode ray tubes with the three primary colors are arranged broadwise in the projection type television stem, it is possible to reduce the breadth in the total system.