There is provided a steering shaft modifier, capable of fundamentally preventing distortion generated in a new steering shaft, being easing aligned, and being simply assembled, including: a frame having a steering shaft penetrating portion formed in a front surface thereof and having a contact surface covering a portion of the steering head and disposed to be in contact with an upper bearing installation portion of a steering shaft installation portion; a shaft including a head portion caught by a lower bearing installation portion of the steering shaft installation portion of the steering head, a body portion passing through the steering shaft installation portion, and a connection portion connected to the frame; and a frame block including a lower contact surface tightly attached to a lower surface of the steering head in the rear of the lower bearing installation portion and coupled to the frame when installed.