Single-wall carbon nanotubes of the smallest diameter formed in microchannel arrays of Zeolite single crystals (IUPAC cord: AFI) have attractive potential for fundamental and device-oriented optical researches. Here we report on very photosensitive characteristics of the material at room temperature. We find that tightly focused irradiation of the 488 nm Ar -ion laser light causes remarkable suppression of the visible emission from nanotubes. The photo-induced suppression occurs under low-level irradiation less than 1 μW. By the nano-tomography performed with Nanofinder, a three-dimensional spectro-tomographic system based on a confocal laser microscope, the size of the affected region is estimated to be 1 μm × 1 μm × 2 μm. This is comparable to the effective volume of the photo-irradiation spot. We discuss the origin of the photo-irradiation effects in view of the effects of the thermal conduction along the tube axis and of the local electronic effects within the photo-irradiated region.