To provide a drainage system, which has a simple structure, cost of which is reduced, in which there is no danger of a leakage of water and the clogging of foreign substances or the like, and from which water can be drained rapidly and easily at a proper time.

The drainage system 1 for the mechanical type parking facility has a water collection tank 5 disposed to the underside of a pallet and opened to the top face of the pallet, a detachable cover 6 disposed to the opening section 4 of the water collection tank 5, water collection ports 12 and a drain inlet 10 formed to the cover 6, and a detachable cap 11 arranged to the drain inlet 10, and the cap 11 is removed at a proper time and water in the water collection tank 5 can be drained by a portable pump 14.