A novel electrical floor-hinge device is provided, which contains an electrical motor and a speed reducing element configured on top of a platform element at a side on top of a body member. A vertical input shaft connected to the speed reducing element is joined to a lateral involute shaft via bevel gears. The involute shaft in turn engages a driven gear on a vertical output shaft. The top end of the output shaft is attached to a seat element whose top surface is fixedly joined to a lower inner corner of a door. By the electrical motor's driving the seat element into clockwise or counterclockwise swing, the door is closed or opened automatically. The speed reducing element can be easily replaced to fit doors of different weight.