Provided is a photodynamic therapy device that enables efficient light irradiation of blood of a patient. A photodynamic therapy device (100) of this disclosure includes a cartridge (10) including a winding core and a tube arranged so as to be wound around the winding core, a casing (50) configured to accommodate the cartridge (10), and a light source (60), which is arranged inside the casing (50), and is configured to irradiate the tube with light. The tube arranged around the winding core has a cross section taken along a direction orthogonal to an extending direction of the tube, which has a first dimension in a first direction and a second dimension in a second direction orthogonal to the first direction. The second dimension is smaller than the first dimension. The second direction is directed outward with respect to the winding core.