Provided are a thickness detection device capable of accurately detecting the thickness of a paper sheet even without intervals between sensors, and an automatic transaction machine. The present invention is provided with: a reference roller unit in which reference rollers are closely aligned in the direction of a predetermined rotating shaft, and rotate with the rotating shaft; a detection roller unit in which closely aligned detection rollers for detecting the thickness of a paper sheet are driven to rotate by the rotation of the respective reference rollers; a conveying unit for conveying the paper sheet between the reference roller unit and the detection roller unit; a sensor unit that generates an AC magnetic field for detection of the paper sheet by the oscillation at a predetermined frequency of a plurality of detection coils that are provided above the respective detection rollers, and detects the amount of displacement of a roller in the generated detection magnetic field based on variations in the magnetic field, the sensor unit having a shape that is longer in the paper sheet conveying direction than in the main scanning direction compared to the detection roller unit; and a calculation unit that calculates the amount of displacement of the paper sheet based on the variations in the magnetic field detected by the sensor unit.