A flush toilet bowl includes: a bowl portion including a pooling portion in communication with a drain conduit; a rim surface provided above the bowl portion; and a first slit opening configured to spout flush water supplied through a first conduit toward the bowl portion and to spout the supplied flush water in a generally tangential direction of the rim surface, thereby generating a swirling flow flowing forward near a boundary between the rim surface and the bowl portion. A slit opening shape in a cross section generally perpendicular to a flow direction of water flow spouted from the first slit opening is horizontally flattened. There is provided a flush toilet bowl capable of minimizing the overhang of the rim portion.