A vehicle door latch device, comprising: an interlocking unit assembly including an interlocking mechanism provided in any one of a door and a vehicle body and configured to be able to hold the door in a closed position by engaging with a striker, which is provided in the other one of the door and the vehicle body and is configured to advance thereto along with closing movement of the door; and an operating unit assembly including an operating mechanism configured to be able to switch over the door between a locked state and an unlocked state, wherein the interlocking unit assembly includes a latch configured to be rotatable to a latched position from an open position via a half closed door position by interlocking with the striker that has advanced thereto, the operating unit assembly includes: a casing, in which the interlocking unit assembly is fitted, and in which the operating mechanism is installed; and a switch plate, on which a half closed door detection switch and an electric wiring connected to the half closed door detection switch are installed, and which is integrally installed in the casing, the half closed door detection switch having a switch pin configured to abut against the latch in the open position and half closed door position or the latch in the latched position and to be pushed in by the latch, and a plane of rotation of the latch and a plate surface of the switch plate intersect each other orthogonally, wherein the latch is configured to directly push in the switch pin. an interlocking unit assembly including an interlocking mechanism provided in any one of a door and a vehicle body and configured to be able to hold the door in a closed position by engaging with a striker, which is provided in the other one of the door and the vehicle body and is configured to advance thereto along with closing movement of the door; and an operating unit assembly including an operating mechanism configured to be able to switch over the door between a locked state and an unlocked state, wherein the interlocking unit assembly includes a latch configured to be rotatable to a latched position from an open position via a half closed door position by interlocking with the striker that has advanced thereto, the operating unit assembly includes: a casing, in which the interlocking unit assembly is fitted, and in which the operating mechanism is installed; and a switch plate, on which a half closed door detection switch and an electric wiring connected to the half closed door detection switch are installed, and which is integrally installed in the casing, the half closed door detection switch having a switch pin configured to abut against the latch in the open position and half closed door position or the latch in the latched position and to be pushed in by the latch, and a casing, in which the interlocking unit assembly is fitted, and in which the operating mechanism is installed; and a switch plate, on which a half closed door detection switch and an electric wiring connected to the half closed door detection switch are installed, and which is integrally installed in the casing, the half closed door detection switch having a switch pin configured to abut against the latch in the open position and half closed door position or the latch in the latched position and to be pushed in by the latch, and a plane of rotation of the latch and a plate surface of the switch plate intersect each other orthogonally, wherein the latch is configured to directly push in the switch pin.