We have detected the [C I]3P1–3P0 emission in the gaseous debris disks, 49 Ceti and β Pictoris, with the Atacama Submillimeter Telescope Experiment (ASTE). The line profiles of [C I] is found to be those of CO(J=3–2) observed with the same telescope as well as the Atacama Large Millimeter/submillimeter Array (ALMA). This result suggests that the atomic carbon (C) coexists with CO in the debris disks, and is likely formed by photodissociation of CO. The C/CO column density ratio is thus derived to be 54±19 to 69±42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of protoplanetary disks, molecular clouds, and diffuse clouds by an order of magnitude. From the result, we suggest that the origin of a large amount of [C I] in the debris disk would likely be a small amount of the H2 molecule in the gas disk. This implies a significant contribution of the secondary gas coming out from dust grains.