A water reuse device for reusing waste water discharged from a bathroom or a kitchen as toilet flushing water, including: a water collecting tank (10); a storage tank (20) receiving the used water stored in the water collecting tank (10) and having a water level sensor (21); a toilet water tank (32) located at a lower level than the storage tank (20) and having a first water level sensor (36) and a second water level sensor (35); a first pipe (22) connecting the storage tank (20) and the toilet water tank (32); a first solenoid valve (40) installed in the first pipe (22); a second pump (38) installed in the toilet water tank (32); a backflow prevention valve (34) provided between the second pipe (33-2) and the third pipe (33-3); and a water shutoff valve (41) provided between a water supply pipe (31) and the water pressure control valve (41-1).