We obtain the projected mass distributions for two Subaru/Suprime-Cam fields in the southwest region (r ≲ 60') of the Coma Cluster (z = 0.0236) by weak-lensing analysis and we detect eight subclump candidates.We quantify the contribution of background large-scale structure (LSS) on the projected mass distributions using Sloan Digital Sky Survey multi-bands and photometric data, under the assumption of mass-to-light ratio for field galaxies.We find that one of the eight subclump candidates, which is not associated with any member galaxies, is significantly affected by LSS lensing. The mean projected mass for the seven subclumps extracted from the main cluster potential is 〈M^(corr)_2D〉 = (5.06 ± 1.30)×10^12 h^−1 M⊙ after an LSS correction. A tangential distortion profile over an ensemble of subclumps is well described by a truncated singular-isothermal spheremodel and a truncated Navarro–Frenk–White model. A typical truncated radius of subclumps, r_t ≃ 35 h^−1 kpc, is derived without assuming any relations between mass and light formember galaxies. The radius coincides well with the tidal radius,∼42 h^−1 kpc, of the gravitational force of the main cluster. Taking into account the incompleteness of the data area, a projection effect, and spurious lensing peaks, it is expected that the mass of the cluster substructures accounts for 19% of the virial mass, with 13% statistical error. The mass fraction of the cluster substructures is in rough agreement with numerical simulations.

N.O. and T.F. are supported in part by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (N.O.: 20740099; T.F.: 20540245) as well as the GCOE program “Weaving Science Web beyond Particle-matter Hierarchy” at Tohoku University and a Grant-in-Aid for Science Research in a Priority Area “Probing theDark Energy through an ExtremelyWide and Deep Survey with Subaru Telescope” (No. 18072001).Y.O. thanks the JSPS Research Fellowships for Young Scientists.