各司其事

Explanation: Secretary: Head of business. Manage their own pool of thing. 　　Source: Ming Feng Meng, "Eastern Zhou Chi," the eighty-fourth back: "Today would have appointed them large ones, being to the Secretary." 　　Examples: Both sides of the lobby, numerous ink volumes piled boxes, bearing the value of clerks, ~. (Qing, Culture and Sport "Heroic Biography" thirty-fifth back)