PURPOSE: To precisely and smoothly focus a photographing lens on a moving object as to an automatic focusing device and focusing method by which the photographing lens is focused on the moving object.

CONSTITUTION: This device is constituted to be provided with a lens driving means 1 changing the extending quantity of the photographing lens, a focus detection means 2 detecting the defocus quantity of an object image surface, an image surface speed calculation means 3 calculating the moving speed of the object image surface with respect to the photographing lens, a lens driving control means 4 controlling the driving means 1 based on the defocus quantity and the moving speed of the object image surface and an adaptive control means 5 reducing instruction quantity corresponding to the defocus quantity given to the control means 4 when the defocus quantity by the detection means 2 and the moving speed of the object image surface by the calculation means 3 are signs showing a relatively reverse direction.