A hinge device of a portable terminal with a foldable structure according to the present invention includes: housing positioned between one end of a first body and one end of a second body; first hinge blade and second hinge blade fixed to the first body and the second body, respectively, and supported against the housing to rotate at a predetermined angle between an ‘unfolded position’ in which the first body and the second body are placed on the same horizontal line and a ‘folded position’ in which the first body and the second body face each other and thus come into contact with each other; and first interlocking gear and second interlocking gear for interlocking the first hinge blade and the second hinge blade with each other so that the first hinge blade and the second hinge blade move relative to each other, wherein the first interlocking gear and the second interlocking gear are mounted on the corresponding housing in such a way as to rotate relative to each other by a predetermined angle around gear shafts by engaging with each other and, on the upper sides of the first interlocking gear and the second interlocking gear a plurality of first gear-side protrusions and second gear-side protrusions are arranged radially in circumferential directions around the gear shafts, and on the undersides of the first hinge blade and the second hinge blade a plurality of first blade-side protrusions and second blade-side protrusions engaging with the first gear-side protrusions and the second gear-side protrusions through rotations are arranged radially in circumferential directions around rotary axes of the first and second hinge blades.