A shrinkable load supporter of a truck includes a telescopic pole set having two end respectively combined with a front base and a rear base and threadably fixed with positioning tubes. Fixed over grooves of the front base and the rear base respectively is a pressing rod, which presses on outer tubes and inner tubes of the telescopic pole set. The pressing rod is provided with plural through holes corresponding to threaded holes of the front base and said rear base. With screws threadably fixed in said through holes of the pressing rod and the threaded holes of the front base and the rear base, the telescopic pole set can thus be firmly combined together with the front base and the rear base.