To provide a temporary cofferdam work caisson capable of securing water pressure control and sufficient cutoff ability, and an installation method therefor.

This temporary cofferdam work caisson 1 formed into a planar annular shape by joining a pair of assembling units 2 in a state faced each other is formed with an engaging recess 10 in the bottom part 9 of each of the assembling units 2, and is installed with a tabular cutoff packing 12 in a front face wall 11 of the engaging recess. The cutoff packing 12 is bent downward to position a bent part 15 in an upper side, and a bent piece 14 bent therein is pressed by a pressing plate 16 from the bottom part 9.