To provide a fitting component mounting structure of a fuel tank with a minimized opening part formed in a resin fuel tank allowing proper attachment of the fitting component to the opening part.

The opening part 24 of the resin fuel tank 20 is formed smaller than an outer diameter of the fitting component (for example, a ventilating valve device 1). A pipe joint 30 is disposed outside of the fuel tank 20 and one connecting end part 31 of the pipe joint 3 is connected with the fitting component through the opening part 24 of the fuel tank 20. At least a part of the pipe joint 30 is coated to be integrally formed, and the pipe joint is connected to the fuel tank 20 by surrounding the opening part 24 of the fuel tank 20.