A method for producing a stainless steel diffusion-bonded product, comprising directly contacting stainless steel materials with each other to unify the materials together by diffusion bonding, wherein at least one of the stainless steel materials to be contacted is a dual-phase steel having a metallic structure of a ferrite phase + carbide, a ferrite phase + a martensite phase or a martensite single phase before being subjected to a diffusion bonding, having the chemical composition below, having a γmax represented by the formula below of 20 to less than 100 and having an austenite transformation starting temperature Ac 1 point of 650 to 950°C during the temperature elevation and having an austenite + ferrite dual-phase temperature region in the range of 880°C or higher, and another one is a steel having the chemical composition, or below, and the diffusion bonding is advanced under conditions such that the vacuum pressure is in the range of 10 -3 Pa or less, the contact surface pressure is in the range of from 0.03 to 1.0 MPa, the heating temperature is in the range of from 880 to 1,080°C and the heating time is in the range from 30 to 120 minutes while being accompanied by the movement of grain boundary caused when the ferrite phase in the dual-phase steel undergoes transformation to an austenite phase, wherein chemical composition consists of from 0.0001 to 0.15% of C, from 0.001 to 1.0% of Si, from 0.001 to 1.0% of Mn, from 0.05 to 2.5% of Ni, from 13.0 to 18.5% of Cr, from 0.005 to 0.1% of N, and optionally of 0.2% or less of Cu, 0.5% or less of Mo, 0.05% or less of Al, 0.2% or less of Ti, 0.2% or less of Nb, 0.2% or less of V, 0.01% or less of B, all in terms of percentage by mass, with the balance of Fe and unavoidable impurities, and having an X value represented by the following formula of 650 to 950: X value = 35 Cr + 1.72 Mo + 2.09 Si + 4.86 Nb + 8.29 V + 1.77 Ti + 21.4 Al + 40.0 B − 7.14 C − 8.0 N − 3.28 Ni − 1.89 Mn- 0.51 Cu + 310 γmax = 420 C − 11.5 Si + 7 Mn + 23 Ni − 11.5 Cr − 12 Mo + 9 Cu − 49 Ti − 50 Nb − 52 Al + 470 N + 189 chemical composition consists of from 0.0001 to 0.15% of C, from 0.001 to 4.0% of Si, from 0.001 to 2.5% of Mn, from 0.001 to 0.045% of P, from 0.0005 to 0.03% of S, from 6.0 to 28.0% of Ni, from 15.0 to 26.0% of Cr, and optionally 7.0% or less of Mo, 3.5% or less of Cu, 1.0% or less of Nb, 1.0% or less of Ti, 0.1% or less of Al, 0.3% or less of N, 0.01% or less of B, 0.5% or less of V, 0.3% or less of W, and 0.1% or less of the total of Ca, Mg, Y and rare earth elements, all in terms of percentage by mass, with the balance of Fe and unavoidable impurities, and chemical composition consists of from 0.0001 to 0.15% of C, from 0.001 to 1.2% of Si, from 0.001 to 1.2% of Mn, from 0.001 to 0.04% of P, from 0.0005 to 0.03% of S, from 11.5 to 32.0% of Cr, and optionally 0.6% or less of Ni, 2.5% or less of Mo, 1.0% or less of Cu, 1.0% or less of Nb, 1.0% or less of Ti, 0.2% or less of Al, 0.025% or less of N, 0.01% or less of B, 0.5% or less of V, 0.3% or less of W and 0.1% or less of the total of Ca, Mg, Y and rare earth elements, all in terms of percentage by mass, with the balance of Fe and unavoidable impurities.