To provide a builtup lamp chimney which is light and low-cost and not bulky for convenient housing and carrying, a lamp chimney assembly where the builtup lamp chimneys are vertically stacked, a lighting unit comprising the builtup lamp chimney, and a flexible sheet for the builtup chimney.

The builtup lamp chimney comprises a tubular body 5 with its upper and lower ends opened which is built up with a single flexible sheet 1. Related to the sheet 1, a locking part is formed on one side 1c of its facing sides while an locking tab 2 which can be detachably engaged with that locking part is formed on the other side 1d. A plurality of support claws 4 which bend toward inside of the tubular body 5 are formed on a sheet side 1b forming the lower end of the tubular body 5 when it is built up.