A sheath flow type flow-cell device for photo-particle-analyzer comprises a substantially flat top surface, at least one first inlet for sheath fluid, at least one first flow passage communicated with the at least one first inlet and contracted toward downstream to be a straight capillary flow passage, a discharge port provided at a terminal end of the straight capillary flow passage, a second inlet for sample fluid, a second flow passage for sample fluid communicated with the second inlet and contracted toward downstream, and coupling portions for sealingly coupling with the particle photo-analyzer. The second flow passage is opened within the at least one first flow passage so as to keep a part of the at least one first flow passage above and below an opening of the second flow passage. The opening is faced in the same direction as the straight capillary flow passage. A wall portion on which the opening locates is rounded. The wall portion is further chamfered and a pair of projections are extended from the wall portion.