An in-vehicle-camera image processing device which performs image processing on a captured image from the outside of a vehicle, comprising: a left camera unit and a right camera unit which are able to selectively switch and output the captured image and a test image; an image-processing unit which performs image processing on the captured image of a left camera image data output from the left camera unit and the captured image of a right camera image data output from the right camera unit that are both input to the image-processing unit; a fault diagnosis unit which performs a fault diagnosis on the left camera unit based on the test image output from the left camera unit and on the right camera unit based on the test image output from the the right camera unit; wherein the image-processing unit determines whether the fault diagnosis is possible based on a result of the image processing, and outputs diagnosis instruction information to the fault diagnosis unit in a case where it is determined that the fault diagnosis is possible; wherein the fault diagnosis unit outputs an image-selection-instruction signal to one of the left and right camera units (201, 202) or sequentially to both camera units (201, 202), for switching the image output from the respective camera unit (201, 202) from the captured image to the test image, in a case where the diagnosis instruction information is input from the image-processing unit; wherein only the left camera unit is switched to the test image, only the right camera unit is switched to the test image, or both camera units (201, 202) are sequentially switched to the test image; and wherein the image-processing unit includes: a plurality of detection processing units which detect external information through the image processing; and a diagnosis possibility determining unit which determines whether the fault diagnosis is possible based on detection processing results of the plurality of detection processing units and predetermined priorities of the plurality of detection processing units. a left camera unit and a right camera unit which are able to selectively switch and output the captured image and a test image; an image-processing unit which performs image processing on the captured image of a left camera image data output from the left camera unit and the captured image of a right camera image data output from the right camera unit that are both input to the image-processing unit; a fault diagnosis unit which performs a fault diagnosis on the left camera unit based on the test image output from the left camera unit and on the right camera unit based on the test image output from the the right camera unit; wherein the image-processing unit determines whether the fault diagnosis is possible based on a result of the image processing, and outputs diagnosis instruction information to the fault diagnosis unit in a case where it is determined that the fault diagnosis is possible; wherein the fault diagnosis unit outputs an image-selection-instruction signal to one of the left and right camera units (201, 202) or sequentially to both camera units (201, 202), for switching the image output from the respective camera unit (201, 202) from the captured image to the test image, in a case where the diagnosis instruction information is input from the image-processing unit; wherein only the left camera unit is switched to the test image, only the right camera unit is switched to the test image, or both camera units (201, 202) are sequentially switched to the test image; and wherein the image-processing unit includes: a plurality of detection processing units which detect external information through the image processing; and a diagnosis possibility determining unit which determines whether the fault diagnosis is possible based on detection processing results of the plurality of detection processing units and predetermined priorities of the plurality of detection processing units. a plurality of detection processing units which detect external information through the image processing; and a diagnosis possibility determining unit which determines whether the fault diagnosis is possible based on detection processing results of the plurality of detection processing units and predetermined priorities of the plurality of detection processing units.