Key input circuit and portable terminal input device

A key input device comprising:

• a wiring substrate;
• and
• a plurality of keys disposed on the wiring substrate and each having three-dimensional displacement surfaces capable of being displaced in a linked fashion relative to one another;
• the three-dimensional displacement surfaces being:
• a preceding displacement surface capable of undergoing a first displacement preceding in time;
• and
• a succeeding displacement surface capable of undergoing a second displacement subsequent in time to the first displacement of the preceding displacement surface;
• the succeeding displacement surface being capable of undergoing the second displacement by a displacing force of the first displacement;
• the plurality of keys each having:
• a first key forming the preceding displacement surface;
• and
• a second key having the succeeding displacement surface;
• a first switching operation being brought about when a first key part of the first key and a first substrate part of the wiring substrate are brought into mechanical contact with each other on the basis of displacement of the preceding displacement surface;
• a second switching operation being brought about when a second key part of the second key and a second substrate part of the wiring substrate are brought into mechanical contact with each other on the basis of displacement of the succeeding displacement surface;
• each of the keys executing the first and second switching operations by movement of its part perpendicular to the substrate surface of the wiring substrate;
• and
• the preceding and succeeding displacement surfaces each forming, before displacement, a convex surface in a direction opposite to the direction of the movement.