To provide a star-delta control device which changes the motor current and torque without step by seamlessly switching star connection and delta connection, and improve comfort for passengers.

A connection control circuit using the star-delta control device is constituted of a delta (Δ) connection 15 and a star (Y) connection 16 which connects windings of a three-phase AC motor 14 (hereinafter simply named 'motor') used for railway cars, an electronic switch 12 which is connected in delta (Δ) connection 15 and star (Y) connection 16 and changes to a delta (Δ) connection 15 or a star (Y) connection 16, and a controller 11 which controls the changeover of the electronic switch 12 according to a bit pattern preliminarily set.