Electrode position detection device and electrode position detection method

An electrode position detection device that, when a negative electrode (30) and a bagged positive electrode (20) having a positive electrode (24) arranged inside a separator (40) formed in a bag shape are layered alternately, detects the relative position of the positive electrode (24) and the negative electrode (30). Said device has: a light source (76) that projects light that penetrates the separator (40) and is reflected by the positive electrode (24) and the negative electrode (30); a camera (84) that receives the light reflected by the positive electrode (24) when the bagged positive electrode (20) is positioned on the uppermost layer and receives the light reflected by the negative electrode (30) when the negative electrode (30) is positioned on the uppermost layer; and a detector (160) that detects the relative position of the positive electrode (24) and the negative electrode (30) on the basis of the results of light reception by the camera (84) when the bagged positive electrode (20) is positioned o