If the floater that controls the water level or the valve connected to the flush gets stuck (i.e. if you drop something in the water tank) the water may continuously flow into the toilet bowl. You can fix the leak by removing it, so check the inside of the water tank first.
If you can not find the problem inside the tank, close the water supply and file an [Inquiry Form] to request a maintenance.
Until the maintenance is performed, close the water supply pipe as described below while you are not using the toilet.