According to one embodiment, a tablet printing apparatus includes: a conveyor belt configured to convey a tablet; a print head configured to perform printing on the tablet conveyed by the conveyor belt; and a belt-position detector configured to detect the position of the conveyor belt in a direction crossing the conveying direction of the tablet in a horizontal plane. The conveyor belt includes a plurality of holes arranged in a row along the conveying direction of the tablet to hold the tablet. The belt-position detector includes an imaging device configured to capture an image of two or more of the holes; and an image processing device configured to detect the position of the conveyor belt in the crossing direction based on the image captured by the imaging device.