A filling machine capable of matching fold lines (m1, m2) preformed on a packing material (11) with actual fold lines (n1, n2) and improving the appearance of a package container (15), comprising a light source (21) for irradiating with light a portion containing at least an overlap portion (S2) out of the outer peripheral surface of a packing material tube (41) provided with the overlap portion (S2), a photodetector for receiving light generated by the light source (21) and reflected off the outer peripheral surface of the packing material tube (41) to generate a sensor output, and an overlap portion detecting/processing means (28) for detecting the overlap portion (S2) by using a peak in the sensor output; a peak is formed in the sensor output of the photodetector because a portion of light reflected off the end of the packing material (11) out of light reflected off the outer peripheral surface of the tube (41) is larger in intensity and therefore a point at which a peak is formed in the sensor output is detected as the overlap portion (S2).