Parallel currents passing between the two strike zones in the scrape-off layer of single-null divertor discharges (SOL current) have been investigated in JT-60U high-density discharges. Under the detached divertor condition and during the X-point MARFE, the in - out asymmetry in electron temperature on the divertor plate was reversed compared with attached cases. At the same time, the direction of the SOL current was also reversed. The observed direction of SOL currents corresponded to the direction of thermoelectric currents, which flow from the high side to the low side. Under the detached divertor condition and during the X-point MARFE, the magnitude of SOL currents at the outboard target was much larger than that at the inboard target, and also than that predicted by the thermoelectric current theory.