A vapor chamber device adapted to be thermally coupled to a heat source includes a first casing and a second casing. The first casing includes a first plate, a first capillary structure at an inner surface of the first plate, and a first lateral wall protruding from the inner surface and surrounding the first capillary structure. The heat source is adapted to contact an outer surface of the first plate. The second casing is stacked on the first casing and includes a second plate, a plurality of supporting posts protruding from the second plate, and a second lateral wall protruding from the second plate and surrounding the supporting posts. The supporting posts face towards the first capillary structure, and the first lateral wall is connected to the second lateral wall. The vapor chamber device includes a second capillary structure disposed between the first capillary structure and the supporting posts, and a third capillary structure disposed in an area which is at the inner surface of the first plate and corresponds to the heat source.