PURPOSE: To prevent the floor of a balcony from being excessively flooded with rainwater.

CONSTITUTION: In a drainage structure of a balcony 4 installed in the periphery of a building body 1 and provided with floors 13A, 13B, 13C, 13D having a drainage slope discharging falled rainwater through a down pipe 3, the first drain ditches 21A-21D are formed on the downstream side of the water inclination on respective floors 13A-13D and the second drain ditch 31C extending from the just underside of the down pipe 3 to the first drain ditch 21C is formed on the floor 13C. Since the rainwater from the down pipe 3 flows in the first drain pitch 21C through the second drain ditch 31C, the floor face of the balcony 4 is prevented from being excessively flooded with the rainwater from the down pipe 3.