Abstract: A power steering apparatus in which a housing to contain a torque sensor for sensing seering torque, a small-sized motor for assisting steering, and a driving device for transmitting driving force of the motor to the steering shaft is made small-sized and disposed on the middle part of the steering shaft in the cab of the car, and, further, pressure angles of rack teeth engaging with a pinion shaft connected to the steering shaft reduce with the advance from the center of the toothed part of the rack to the end thereof so that steering assisting power is increased with the increase in the degree of steering angle.