A method of inspecting whether a printed board is appropriately supported by a supporting device, when a holding device holding an electric component mounts the electric component on the printed board supported by the supporting device, the method including the steps of taking, with an image taking device, an image of at least one prescribed detection portion of the printed board supported by the supporting device, and judging, based on image data representing the taken image of the detection portion, whether the printed board is appropriately supported by the supporting device.