A stainless steel slab containing B, wherein a protecting material is joined onto at least two faces across the bloom from each other in a stainless steel bloom containing B of 0.3–2.5 mass %, being integrated into one-piece by forming a weld metal comprising a stainless steel with chemical composition that satisfies the relationship expressed by following formulas (1)–(4), and a method to produce a steel product by rolling said slab. Further, it is preferable to interpose an insert material between above stainless steel bloom and above protecting material in bonding process. 15≦Cr eq≦30,  (1) 4≦Cr eq−Ni eq≦17,  (2) Cr eq=Cr+1.5 Si+Mo−5 B,  (3) Ni eq=Ni+30 (C+N)+0.5 Mn  (4) Herein, each symbol of a chemical element designates the content (mass %) of relevant chemical element contained in steel. Accordingly, it makes it possible to subject a stainless steel slab containing B to hot working without generating edge cracking, so as to be used as a source material of a neutron shielding container and a separator of a fuel cell.