A structure of a cylindrical boss forming place of a cabinet is provided. A resin-molded plate has a first face which is flat and a second face which is opposite to the first face. A resin-molded boss is formed into a cylindrical shape and is integrally protruded from the second face of the plate. A thickness t of a cylinder wall at a base end of the boss is less than a reference thickness T of the plate. When the plate is divided into a circular-shaped first area partly defining an inner space of the cylindrical boss, a ring-shaped second area disposed to around the first area so as to correspond to the cylinder wall and a peripheral third area disposed to surround the second area, the peripheral third area is formed such that a thickness of the third area is equal to the thickness t of the cylinder wall at an innermost portion, the thickness of the third area increases from the inside to the outside, and the thickness of the third area is equal to the reference thickness T of the plate at an outermost portion, and the circular-shaped first area is formed such that a thickness T1 of the first area is less than 0.6 times the thickness t of the cylinder wall.