An image processing apparatus includes: a conveyance unit configured to convey a medium; a sensor configured to sense a medium being conveyed; and a controller configured to control the conveyance unit and acquire a result of the sensing performed by the sensor. The sensor includes a light emitter, a light receiver configured to perform output in accordance with the amount of the received light, and a shielding unit including a transmissive part through which the sensing light transmits. The transmissive part has a shape in which an opening width in a direction orthogonal to a conveyance direction of the medium changes in the conveyance direction. The controller determines skewing of the medium being conveyed based on change in the amount of light received by the light receiver as the medium passes along the transmissive part and temporal change in accordance with the conveyance of the medium.