An exhaust gas purifier for an internal combustion engine having a plurality of cylinder groups, comprising: a plurality of exhaust passages (11A, 11B) connected to the respective cylinder groups; a plurality of exhaust purifying units (17A, 17B) arranged in the respective exhaust passages (11A, 11B) and configured to collect particulate matter discharged from the internal combustion engine; a plurality of regenerating means (20A, 20B) to supply fuel to the respective exhaust purifying units (18A, 18B) to burn the particulate matter accumulated in the respective exhaust purifying units (19A, 19B), thereby to regenerate the exhaust purifying units (19A, 19B); a plurality of accumulation amount detecting means (21A, 21B) to detect particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B); regeneration temperature determining means which, in regeneration of the plurality of exhaust purifying units (19A, 19B) by the plurality of regenerating means (20A, 20B), determines target regeneration temperatures of the respective exhaust purifying units (19A, 19B), based on the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) detected by the respective accumulation amount detecting means (2 1 A, 2 1 B); controlling means to control each of the regenerating means (20A, 20B) according to the target regeneration temperatures of the respective exhaust purifying units (19A, 19B) determined by the regeneration temperature determining means, when the accumulation amount detecting mean (21A, 21B) detect that the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) reach a regeneration start threshold; and determination means to determine whether the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) detected by the respective accumulation amount detecting means (21A, 21B) are smaller than a predetermined amount, characterized in that the regeneration temperature determining means has temperature changing means which, when the determination means determines that the particulate matter accumulation amount in the exhaust purifying unit (19A, 19B) is smaller than the predetermined amount, decreases the target regeneration temperature of the exhaust purifying unit (19A, 19B) for which the particulate matter accumulation amount is determined to be smaller than the predetermined amount, to within a temperature range available for the regeneration of the exhaust purifying units (19A, 19B). a plurality of exhaust passages (11A, 11B) connected to the respective cylinder groups; a plurality of exhaust purifying units (17A, 17B) arranged in the respective exhaust passages (11A, 11B) and configured to collect particulate matter discharged from the internal combustion engine; a plurality of regenerating means (20A, 20B) to supply fuel to the respective exhaust purifying units (18A, 18B) to burn the particulate matter accumulated in the respective exhaust purifying units (19A, 19B), thereby to regenerate the exhaust purifying units (19A, 19B); a plurality of accumulation amount detecting means (21A, 21B) to detect particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B); regeneration temperature determining means which, in regeneration of the plurality of exhaust purifying units (19A, 19B) by the plurality of regenerating means (20A, 20B), determines target regeneration temperatures of the respective exhaust purifying units (19A, 19B), based on the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) detected by the respective accumulation amount detecting means (2 1 A, 2 1 B); controlling means to control each of the regenerating means (20A, 20B) according to the target regeneration temperatures of the respective exhaust purifying units (19A, 19B) determined by the regeneration temperature determining means, when the accumulation amount detecting mean (21A, 21B) detect that the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) reach a regeneration start threshold; and determination means to determine whether the particulate matter accumulation amounts in the respective exhaust purifying units (19A, 19B) detected by the respective accumulation amount detecting means (21A, 21B) are smaller than a predetermined amount, characterized in that the regeneration temperature determining means has temperature changing means which, when the determination means determines that the particulate matter accumulation amount in the exhaust purifying unit (19A, 19B) is smaller than the predetermined amount, decreases the target regeneration temperature of the exhaust purifying unit (19A, 19B) for which the particulate matter accumulation amount is determined to be smaller than the predetermined amount, to within a temperature range available for the regeneration of the exhaust purifying units (19A, 19B).