The present invention provides as an object a novel hinge device which is extremely valuable as a commercial product and an electronic instrument using the hinge device. A hinge device for pivoting a first member (1) and a second member (2) to be rotatably opened and closed is characterized in that when the second member (2) kept under a coupled and closed condition is opened to the first member (1), in a rotational range A1 from the coupled and closed position P1 to a predetermined open angle position P2 rotated in an open direction, a closing rotational biasing effect is generated for automatically closing the second member (2) to the coupled and closed position P1 relative to the first member (1), and when the second member (2) is manually rotated in the open direction exceeding the predetermined open angle position P2 to the first member (1), an open rotational biasing effect is generated for automatically opening the second member (2) to a predetermined open angle position P3 relative to the first member (1).