A method for forming hydraulic oil passages for hydraulic actuators according to an aspect of the present invention includes: forming a valve block mount surface including first and second regions on an outer surface of a housing; collecting valves for hydraulic actuators belonging to a main function group to a main function valve block that is mountable directly or indirectly on the first region; collecting valves for hydraulic actuators belonging to an additional function group to an additional function valve block that is mountable directly or indirectly on the second region; and mounting the valve blocks on corresponding regions of the valve block mount surface, and thereby, the hydraulic actuators to be mounted are fluidly connected to each other so that the hydraulic actuators are operable by using hydraulic oil from a common oil source.