A toilet bowl flushing device capable of reliably discharging excreta with less flush water in a short time and emitting low flushing noise. The toilet bowl flushing device has first water supply means for supplying flush water to a bowl (2) of a toilet bowl body (1), second water supply means for additionally supplying the flush water, a drain flow passage (5) connected to the downstream side ofthe water sealing part (4) of the toilet bowl body (1), air suction means for sucking air from the drain flow passage (5), and a control device (50) for controlling the first and second water supply means and the air suction means. The first water supply means is formed so that it can supply the flush water from the rear of the bowl (2) so as to form a swirl flow in the bowl (2). The second watersupply means has a cistern (20) and discharge means for discharging the flush water in the cistern (20) to the bowl (2) when an open/close valve (V2) is opened. After activating the first water supply means, the control device (50) activates the air suction means, creating a siphon effect to form the swirl flow, and then opens the open/close valve (V2) after the swirl flow is formed and before the siphon effect is completed.