A high strength steel plate for sour-resistant line pipes comprising: a chemical composition containing, by mass%, C: 0.02 % to 0.08 %, Si: 0.01 % to 0.50 %, Mn: 0.50 % to 1.80 %, P: 0.001 % to 0.015 %, S: 0.0002 % to 0.0015 %, Al: 0.01 % to 0.08 %, and Ca: 0.0005 % to 0.005 %, optionally at least one selected from the group consisting of Cu: 0.50 % or less, Ni: 0.50 % or less, Cr: 0.50 % or less, and Mo: 0.50 % or less, Nb: 0.005 % to 0.1 %, V: 0.005 % to 0.1 %, and Ti: 0.005 % to 0.1 %, with the balance being Fe and inevitable impurities, wherein in a cross-section perpendicular to a rolling direction of the steel plate, the number of Mn-concentrated spots that are approximated to an elliptical shape having a major axis length of more than 1.5 mm is 3 or less per 100 mm in length in a plate width direction, in three regions centering on each of the three points at the plate thickness center of the steel plate and ranging ± 5 mm in the plate thickness direction and ± 200 mm in the plate width direction at a W/4 position, a W/2 positon and a 3W/4 position from one end in the plate width direction of the steel plate, where W denotes the plate width, and where the Mn-concentrated spot is defined as a site in which the Mn concentration is 1.60% or more when the Mn content in the steel plate is 1.50% or less, and as a site in which the Mn concentration is at least 0.10 % higher than the Mn content in the steel plate when the Mn content in the steel plate is more than 1.50 % and 1.80% or less, where, in the cross-section perpendicular to the rolling direction of the steel plate, centering on the plate thickness center at the W/4 position, the W/2 position, and the 3W/4 position (total of three points) in the plate width direction, test pieces of 20 mm thick and 20 mm wide are collected, and from each of the three test pieces thus obtained, three samples are collected, and a total of nine samples are subjected to hydrogen-induced cracking resistance examination, HIC resistance of all the nine samples are 10 % or less in terms of CAR and where the CAR is measured according to NACE TM0284, variation in the HIC resistance in the plate width direction in terms of 3σ is 5 % or less when σ denotes a standard deviation of CARs of the nine samples, and a tensile strength is 520 MPa or more, where the tensile strength is measured according to API-5L. in a cross-section perpendicular to a rolling direction of the steel plate, the number of Mn-concentrated spots that are approximated to an elliptical shape having a major axis length of more than 1.5 mm is 3 or less per 100 mm in length in a plate width direction, in three regions centering on each of the three points at the plate thickness center of the steel plate and ranging ± 5 mm in the plate thickness direction and ± 200 mm in the plate width direction at a W/4 position, a W/2 positon and a 3W/4 position from one end in the plate width direction of the steel plate, where W denotes the plate width, and where the Mn-concentrated spot is defined as a site in which the Mn concentration is 1.60% or more when the Mn content in the steel plate is 1.50% or less, and as a site in which the Mn concentration is at least 0.10 % higher than the Mn content in the steel plate when the Mn content in the steel plate is more than 1.50 % and 1.80% or less, where, in the cross-section perpendicular to the rolling direction of the steel plate, centering on the plate thickness center at the W/4 position, the W/2 position, and the 3W/4 position (total of three points) in the plate width direction, test pieces of 20 mm thick and 20 mm wide are collected, and from each of the three test pieces thus obtained, three samples are collected, and a total of nine samples are subjected to hydrogen-induced cracking resistance examination, HIC resistance of all the nine samples are 10 % or less in terms of CAR and where the CAR is measured according to NACE TM0284, variation in the HIC resistance in the plate width direction in terms of 3σ is 5 % or less when σ denotes a standard deviation of CARs of the nine samples, and a tensile strength is 520 MPa or more, where the tensile strength is measured according to API-5L.