A dimension measurement apparatus, comprising: a camera configured to photograph an object to be measured to generate a distance image of the object to be measured; and a processing device configured to generate dimension data indicating a length, a width, and a height of the object to be measured, based on the distance image generated by the camera; the processing device having a memory to store a control program for generating the dimension data and a controller; the controller executing the control program, to acquire the distance image of the object to be measured, whereby the distance image generated by the camera is expressed by point group data including positions of respective pixels in a three-dimensional XYZ coordinate space such that the distance image is an XYZ-coordinate image, characterized in the controller further executing the control program, to divide the acquired distance image into an X coordinate image, a Y coordinate image, and a Z coordinate image, to remove coordinate points not corresponding to a reference surface of the object to be measured, in the respective divided X coordinate image, Y coordinate image, and Z coordinate image, to generate an X coordinate image of the reference surface, a Y coordinate image of the reference surface, and a Z coordinate image of the reference surface, and to generate the dimension data indicating the length, the width, and the height of the object to be measured, based on the respective generated coordinate images of the reference surface; whereby the controller performs an X coordinate image processing which removes X coordinate points in a range not corresponding to the reference surface from the divided X coordinate image, to generate the X coordinate image of the reference surface; the controller performs a Y coordinate image processing which removes Y coordinate points in a range not corresponding to the reference surface from the divided Y coordinate image, to generate the Y coordinate image of the reference surface; and the controller performs a Z coordinate image processing which removes coordinate points in a range not corresponding to the reference surface from the divided Z coordinate image, to generate the Z coordinate image of the reference surface. a camera configured to photograph an object to be measured to generate a distance image of the object to be measured; and a processing device configured to generate dimension data indicating a length, a width, and a height of the object to be measured, based on the distance image generated by the camera; the processing device having a memory to store a control program for generating the dimension data and a controller; the controller executing the control program, to acquire the distance image of the object to be measured, whereby the distance image generated by the camera is expressed by point group data including positions of respective pixels in a three-dimensional XYZ coordinate space such that the distance image is an XYZ-coordinate image, characterized in the controller further executing the control program, to divide the acquired distance image into an X coordinate image, a Y coordinate image, and a Z coordinate image, to remove coordinate points not corresponding to a reference surface of the object to be measured, in the respective divided X coordinate image, Y coordinate image, and Z coordinate image, to generate an X coordinate image of the reference surface, a Y coordinate image of the reference surface, and a Z coordinate image of the reference surface, and to generate the dimension data indicating the length, the width, and the height of the object to be measured, based on the respective generated coordinate images of the reference surface; whereby the controller performs an X coordinate image processing which removes X coordinate points in a range not corresponding to the reference surface from the divided X coordinate image, to generate the X coordinate image of the reference surface; the controller performs a Y coordinate image processing which removes Y coordinate points in a range not corresponding to the reference surface from the divided Y coordinate image, to generate the Y coordinate image of the reference surface; and the controller performs a Z coordinate image processing which removes coordinate points in a range not corresponding to the reference surface from the divided Z coordinate image, to generate the Z coordinate image of the reference surface.