Abstract: A water closet having a trap drainage exit in a wall above a floor, in which at the time of flushing, a vent space is partitioned in a wall-like manner by water falling from a weir. A rise in the water level of a sump portion of the trap results, and air within the trap is quickly forced toward the drainage exit side by the force of the water flow to cause the interior of the trap drainage to have a decreased pressure so that siphon action easily occurs. When the feed rate of water from a tank slows, to terminate the siphon action, air is promptly introduced into the siphon area from a notch in a partitioning wall, whereby the air introduction is hastened and the siphon effect is terminated quickly.