A chain elongation detection device capable of precisely measuring the amount of elongation in a chain is obtained. A chain elongation detection device that detects elongation of a chain (1) in a transmission device provided with a drive sprocket (2), a driven sprocket (3), and a chain (1) that is wound around the drive sprocket (2) and the driven sprocket (3) and that transmits motive power of the drive sprocket (2) to the driven sprocket (3), wherein the chain elongation detection device is provided with: a meshing height measurement device (4) that measures the meshing height of the chain (1) within the range in which the driven sprocket (3) and the chain (1) mesh; and a signal processing device (5) that, using a signal acquired by the meshing height measurement device (4), determines the difference in height between adjacent rollers (15) in the chain (1) and estimates the amount of elongation in the chain (1) from the determined height difference.
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