Structure of control valve body of automatic transmission has valve body enclosures having channels on opposing surfaces thereof; a separate plate sandwiched between the valve body enclosures for defining oil passages on both sides of the separate plate; and an orifice provided at the separate plate. The oil passages on both sides of the separate plate, which are upstream and downstream side oil passages located on upstream and downstream sides of the separate plate, communicate with each other through the orifice. Depth h, in a part facing to the orifice, of the channel corresponding to the downstream side oil passage is set to be shallower than depth of the channel corresponding to the upstream side oil passage, and the depth h of the channel in the part facing to the orifice and a diameter d of the orifice are set so as to satisfy relationship of h≤3d.