According to one embodiment, a sheet type determination apparatus includes a tray, light source, detection unit, database, and operation unit. The tray is configured to hold a sheet bundle formed by stacked sheets. The light source emits illumination light to a first region. The detection unit detects a light intensity distribution of transmitted light emerging from a second region. The transmitted light is generated as the illumination light passes through the sheet bundle, and the second region is different from the first region. The database stores a table describing a relation between reference attenuation rates and types. The operation unit is configured to calculate an attenuation rate of the transmitted light based on the light intensity distribution, and determine a type of the sheets by comparing the attenuation rate with the reference attenuation rates.