The present invention provides a hinge mechanism capable of suppressing an increase in manufacturing man-hours. A hinge mechanism (1) has: a body side hinge member (10, a structure side hinge) including an upper mounting portion (11a, a first mounting portion) and a lower mounting portion (11b, a second mounting portion), wherein the structure side hinge member is attached to a structural body (S,structural body) via the upper mounting portion and the lower mounting portion; door side hinge (20, an opening and closing side hinge member) is attached to the door (S2, an opening and closing body); and a pivot structure (30) that pivotably supports the structure side hinge member (10) and the opening and closing side hinge member (20) so that the structure side hinge member and the opening and closing side hinge member are allowed to pivot relative to each other. The structure side hinge member is made of a single plate-like member (10). The pivot structure (30) is located between the upper mounting portion and the lower mounting portion.