A gauge line position measuring device measures a position of a gauge line provided on a test piece by a non-contact video method. The measuring device includes a gauge line mark adapted to be provided on the test piece and has the gauge line and a first continuous harmonious color density arranged line-symmetrically with respect to the gauge line, and a video camera for taking an image of the gauge line mark on the test piece and outputting gauge line mark image data. A calculation device calculates a gauge line position based on the gauge line mark image data.