To provide a system for automatically switching the feed voltage polarity to a rail by detecting the running of a railway model rolling stock.

Such functions are provided as; detecting whether there is a railway model rolling stock or not on the rail constituting blocked sections by a circuit for detecting the electric current generated by the running of the railway model rolling stock, etc.; retaining the connection of the output of a DC power supply device to the rail in a blocked section where the railway model rolling stock is running on the railway; cutting the connection of the output of the DC power supply device to the rail in a blocked section where the railway model rolling stock is not present on the railway; switching the positive/negative polarity to connect the output of the DC power supply device to the rail in a blocked section where the railway model rolling stock enters so that the railway model rolling stock can keep running in the same direction as in the blocked section where the railway model rolling stock ran before the entrance; and cutting the connection of the output of the DC power supply device to the rail in the blocked section where the railway model rolling stock passed and there is no railway model rolling stock on the railway.