The present invention relates to an accumulation of water discharge device of the fluidized-bed reactor in which while continuing to run uninterrupted operation the accumulated water from accumulating in the windbox and the distributor plate the lower gas supply pipe to the fluidized-bed reactor removed using a furnace gas pressure, in the fluidized-bed reactors installed dust in the lower distribution plate windbox (windbox) of which is mounted inclined to have a predetermined angle to flow down by its own weight and the inclined portion; The distributor plate in the gas supply pipe connected to the lower portion, and one end is connected to a position where dust is accumulated, the other end is connected to the rapid cooling water discharge pipe with the accumulation; The water discharge pipe is mounted in a stacked configuration and including a running water discharge control valve to control the amount of water accumulated discharged to the rapid cooling from the gas supply pipe through the accumulated water discharge pipe as the opening.