Who should be responsible for the bidding activities of construction projects according to law?

Who is in charge of this project? For example, with the approval of the National Development and Reform Commission and other departments, Company A is the project owner and construction unit, which can also be called Party A. Company A is responsible for the bidding of design, construction and installation projects, equipment and materials involved in the project. He can do it himself, or entrust a bidding agency to complete all kinds of bidding for design units, construction units and equipment. Personal opinion, for reference only.