The rotational spectral lines (JN=32-21 and JN=21-10) of 13CCS and C13CS have been observed toward a cold dark cloud, TMC-1. The strongest hyperfine component lines of 13CCS and C13CS (JN=21-10, F=5/2-3/2) have successfully been detected. The [C13CS/[13CCS abundance ratio is determined to be 4.2+/-2.3 (3 σ). The [CCS/[13CCS ratio is evaluated to be 230+/-130 (3 σ), and hence, 13CCS is found to be significantly diluted. Such a difference between the 13CCS and C13CS abundances is also found in L1521E, which is a very young core with rich carbon-chain molecules. Therefore, the anomaly is not specific to TMC-1, but seems to be common for the CCS-rich clouds. Furthermore, we have also observed the J=4-3 transition of 13CCCS and CCC34S in TMC-1 and L1521E and have found that the [CCC34S/[13CCCS ratio is larger than 8.4 (3 σ). This lower limit is considerably larger than the interstellar [12C[34S/[13C[32S ratio of 3, indicating that 13CCCS is diluted as in the case of 13CCS. These results give us strong constraints on the main pathways to produce CCS and CCCS.