When current collecting wires are laid in parallel with each other on a solar cell on which a photosensitive film is formed, a wire tension adjusting mechanism is provided which includes a bobbin holder shaft pivotally held on the side of a frame in a bobbin cassette in a wiring apparatus and a wire bobbin is detachably fixed on the bobbin holder shaft. The wire tension adjusting mechanism further includes a pre-load means for adjusting the torque of the bobbin holder shaft and the tension of each current collecting wire to be drawn out from the wire bobbin held by the bobbin shaft is adjusted.