A clad steel plate comprising: a base steel plate; and a cladding metal made of a corrosion-resistant alloy of an austenitic stainless steel, an austenitic-ferritic duplex stainless steel or a nickel-based alloy bonded or joined to one surface of the base steel plate, wherein the base steel plate comprises: a chemical composition containing, in mass%, C: 0.02 % to 0.10 %, Si: 1.00 % or less, Mn: 0.50 % to 2.00 %, P: 0.030 % or less, and S: 0.020 % or less, optionally, in mass%, at least one selected from the group consisting of Ni: 0.01 % to 1.00 %, Cr: 0.01 % to 0.50 %, Mo: 0.01 % to 0.50 %, V: 0.001 % to 0.100 %, Nb: 0.005 % to 0.050 %, Ti: 0.005 % to 0.100 %, Al: 0.005 % to 0.200 %, Cu: 0.01 % to 0.70 %, Ca: 0.0003 % to 0.0050 %, B: 0.0003 % to 0.0030 %, and REM: 0.0003 % to 0.0100 %, with the balance consisting of Fe and inevitable impurities, where Ceq is 0.20 to 0.50, Ceq being defined by: Ceq = C + Mn/6 + Cu + Ni / 15 + Cr + Mo + V / 5 where C, Mn, Cu, Ni, Cr, Mo, and V are contents in mass% of the corresponding elements in the chemical composition of the base steel plate, a microstructure of a surface portion containing, in terms of area fraction, at least one of a bainite phase or a martensite phase in an amount of 80 % or more in total; and a microstructure of an inner portion containing, in terms of area fraction, a ferrite phase in an amount of 30 % or more, and the difference in hardness between the surface portion and the inner portion of the base steel plate is 25 or more to 80 or less in terms of Vickers hardness, where the microstructure and the hardness of the surface portion of the base steel plate are ones measured at a position of 1 mm in depth in a thickness direction from another surface of the base steel plate on a side not bonded or joined to the cladding metal, and the microstructure and the hardness of the inner portion of the base steel plate are ones measured at a position of 1 mm in depth in the thickness direction from an interface between the base steel plate and the cladding metal bonded or joined together, wherein the microstructure is measured as an average of occupied area fractions of each phase in 10 observation fields imaged with a scanning electron microscope where the each phase is identified through an image interpretation, and wherein the difference in hardness is measured as a result of subtracting a hardness of the inner portion from a hardness of the surface portion where the hardness is measured by a Vickers test in accordance with JIS Z 2244 with a test load of 10kgf. C: 0.02 % to 0.10 %, Si: 1.00 % or less, Mn: 0.50 % to 2.00 %, P: 0.030 % or less, and S: 0.020 % or less, Ni: 0.01 % to 1.00 %, Cr: 0.01 % to 0.50 %, Mo: 0.01 % to 0.50 %, V: 0.001 % to 0.100 %, Nb: 0.005 % to 0.050 %, Ti: 0.005 % to 0.100 %, Al: 0.005 % to 0.200 %, Cu: 0.01 % to 0.70 %, Ca: 0.0003 % to 0.0050 %, B: 0.0003 % to 0.0030 %, and REM: 0.0003 % to 0.0100 %, a microstructure of a surface portion containing, in terms of area fraction, at least one of a bainite phase or a martensite phase in an amount of 80 % or more in total; and a microstructure of an inner portion containing, in terms of area fraction, a ferrite phase in an amount of 30 % or more, and the difference in hardness between the surface portion and the inner portion of the base steel plate is 25 or more to 80 or less in terms of Vickers hardness, where the microstructure and the hardness of the surface portion of the base steel plate are ones measured at a position of 1 mm in depth in a thickness direction from another surface of the base steel plate on a side not bonded or joined to the cladding metal, and the microstructure and the hardness of the inner portion of the base steel plate are ones measured at a position of 1 mm in depth in the thickness direction from an interface between the base steel plate and the cladding metal bonded or joined together, wherein the microstructure is measured as an average of occupied area fractions of each phase in 10 observation fields imaged with a scanning electron microscope where the each phase is identified through an image interpretation, and wherein the difference in hardness is measured as a result of subtracting a hardness of the inner portion from a hardness of the surface portion where the hardness is measured by a Vickers test in accordance with JIS Z 2244 with a test load of 10kgf.