The purpose of the present invention is to provide a key operation detection device (5) that can suppress occurrences of chattering caused by slipping and floating between a fixed side contact surface (10a) and a movable side contact point (9a) and can maintain a stable contact state for the contact point. Provided is a key operation detection device (5), which is provided with a fixed side contact surface (10a) formed on a substrate (10) provided in a frame (2) wherein the key (4) is supported freely rotatably, a base unit (6) provided in the frame (2), a dome unit (7) protruding from the base unit (6), a top unit (8) provided on the protruding side end of the dome unit (7), and a movable side contact point (9a) provided on the top unit (8), and in which the fixed side contact surface (10a) and the movable side contact point (9a) are in contact by means of elastic deformation of the dome unit (7) and thereby an operation signal for a key (4) is transmitted. A base end side plane (BP) that includes lines of intersection for the base unit (6) and the dome unit (7) and a tip end side plane (TP) that includes intersecting lines for the dome unit (7) and the top unit (8) intersect on the rotational axis (3a) side of the key (4), and a contact point side plane (CP) that includes the fixed side contact surface (10a) and the base end side plane (BP) intersect at the rotational axis (3a) of the key (4).