A switch assembly of a vehicle door latch device, the switch assembly includes: a latch switch detecting a position of a latch, the latch being pivotally supported by a latch shaft to be engaged with a striker; a ratchet switch that detecting a position of a ratchet, the ratchet being pivotally supported by a ratchet shaft to be engaged with the latch and prevented reverse rotation of the latch; and a one common switch case that the latch switch and the ratchet switch are installed in the one common switch case. The latch shaft and the ratchet shaft are arranged to be isolated across a striker moving trajectory of the striker. The one common switch case is arranged on a latch body on one side of a striker moving trajectory.