A coordinate input device, comprising: an operation plate that is cantilevered and flexibly supported; a touch sensor; a circuit board that is disposed to provide a predetermined gap and includes a push-in input switch; and a casing that includes an upper cover section and a lower cover section and accommodates the touch sensor and the circuit board inside a space formed by the upper cover section and the lower cover section, wherein the casing includes the operation plate, a support plate, and a starting point forming section, wherein the operation plate and the support plate constitute the upper cover section of the casing, and wherein the support plate cantilevers and flexibly supports the operation plate, wherein the casing has a form that allows a portion including the support plate to be graspable by a user, the support plate is disposed at a position that is touchable with a base of a thumb of the user, upon grasp of the casing by the user, and the operation plate is disposed at a position that is touchable with a tip of the thumb of the user, upon grasp of the casing by the user, wherein the touch sensor is attached to a rear surface of the operation plate, in that the gap is provided between the circuit board and the touch sensor, and in that the starting point forming section is disposed below the support plate and forms a starting point of displacement in the support plate, wherein the support plate is fixed to the lower cover section below the support plate through the starting point forming section, wherein the starting point forming section comprises a female screw section, an intermediate substrate, and a male screw, wherein the female screw section is provided in a rear surface of the support plate, the intermediate substrate is fixed to the lower cover section and includes an opening at a position that faces the female screw section, and the male screw is configured to be fitted in the female screw section through the opening, and in that the operation plate constitutes, in the casing, an inclined plane descending as is farther away from the support plate, and the circuit board is disposed to allow a width of the gap to be uniform in a plane when no load is being applied to the upper cover section. an operation plate that is cantilevered and flexibly supported; a touch sensor; a circuit board that is disposed to provide a predetermined gap and includes a push-in input switch; and a casing that includes an upper cover section and a lower cover section and accommodates the touch sensor and the circuit board inside a space formed by the upper cover section and the lower cover section, wherein the casing includes the operation plate, a support plate, and a starting point forming section, wherein the operation plate and the support plate constitute the upper cover section of the casing, and wherein the support plate cantilevers and flexibly supports the operation plate, wherein the casing has a form that allows a portion including the support plate to be graspable by a user, the support plate is disposed at a position that is touchable with a base of a thumb of the user, upon grasp of the casing by the user, and the operation plate is disposed at a position that is touchable with a tip of the thumb of the user, upon grasp of the casing by the user, wherein the touch sensor is attached to a rear surface of the operation plate, in that the gap is provided between the circuit board and the touch sensor, and in that the starting point forming section is disposed below the support plate and forms a starting point of displacement in the support plate, wherein the support plate is fixed to the lower cover section below the support plate through the starting point forming section, wherein the starting point forming section comprises a female screw section, an intermediate substrate, and a male screw, wherein the female screw section is provided in a rear surface of the support plate, the intermediate substrate is fixed to the lower cover section and includes an opening at a position that faces the female screw section, and the male screw is configured to be fitted in the female screw section through the opening, and in that the operation plate constitutes, in the casing, an inclined plane descending as is farther away from the support plate, and the circuit board is disposed to allow a width of the gap to be uniform in a plane when no load is being applied to the upper cover section.