Abstract: According to one embodiment, an ultrasonic detecting device includes a transmitter arranged at a predetermined angle with respect to a conveying plane on which a sheet is conveyed, the transmitter emitting ultrasonic waves towards the conveying plane; a receiver provided with a plurality of channels for detecting the ultrasonic waves, the receiver detecting the ultrasonic waves incident on the channels; and a dividing member to shield the receiver from diffraction waves of the ultrasonic waves emitted from the transmitter, the diffraction waves being diffracted at an edge of the sheet that delimits the sheet in a direction perpendicular to a conveying direction of the sheet.

Abstract: According to one embodiment, an ultrasonic line sensor includes a plurality of ultrasonic sensors each comprising a circular vibrating surface and generating an electrical signal in accordance with an ultrasonic wave that enters the vibrating surface; and at least one sound absorbing member that is provided between the vibrating surfaces of the ultrasonic sensors and a detection target, and that absorbs an ultrasonic wave, the sound absorbing member being arranged in a position where the sound absorbing member overlaps both edge portions of the vibrating surfaces in a scanning direction that is perpendicular to a conveying direction of the detection target such that effective regions, which are regions in the vibrating surfaces not overlapped by the sound absorbing member, each have two sides parallel to the conveying direction of the detection target.