Abstract: A treatment apparatus and a treatment method capable of minimally invasively specifying a lesion extent and checking progress of treatment while performing the treatment for destroying tumor cells. The treatment apparatus that detects and destroys a tumor cell by irradiating an antibody-photosensitive substance adsorbed on a tumor cell membrane with excitation light includes: an elongated tubular shaft having optical transparency; a light irradiation unit configured to emit the excitation light of the antibody-photosensitive substance from an inside of the shaft in a side direction perpendicular to an axial direction of the shaft; and a side direction fluorescence detection unit configured to detect, from the side direction perpendicular to the axial direction of the shaft, fluorescence emitted by the excited antibody-photosensitive substance, and movable in the axial direction with respect to the shaft.