A touch sensor device comprises: a touch sensor 1 for sending out an output voltage signal S1 representing the presence or absence of an operation; an operation presence/absence determination unit 2 which, when the output voltage signal has a value equal to or more than a predetermined threshold value, determines that the operation has occurred; a stability determination unit 5 for detecting whether a differential signal S3 representing a differential value obtained by differentiating the output voltage signal is limited within a predetermined range or not; and a count-up timer 4 which, when a period during which the differential signal is limited within the predetermined range becomes a predetermined time period or longer on the premise that the output voltage signal has the value equal to or more than the predetermined threshold value, sends out an ON determination signal S5 and allows an external device 7 to operate.