A hinge mechanism of a button cover of an electronic apparatus includes a pair of modules installed adjacent each other in respective receiving spaces of a case body. Each module includes: a hinge housing; a hinge shaft having a shaft on a first end thereof and a protrusion on a second end thereof and being inserted into the hinge housing so that said first end is disposed outward; a cam hinge having an indent and a protrusion on the same one end thereof so that the protrusion is engaged with the indent; a hinge cover having a hooking protrusion to be coupled to the hinge housing; and a coil spring installed between the cam hinge and the hinge cover. The shaft is coupled to the button cover so that the cover is opened and shut by the action of the pair of modules.