A regeneration control device controlling a temperature increase unit of an exhaust gas treatment device including a DOC disposed in an exhaust passage of a diesel engine to regenerate the exhaust gas treatment device, the regeneration control device comprising: a DOC temperature-increase-necessary-state detection part configured to detect a temperature increase necessary state including at least one of a blockage state of the DOC or a blockage risk state of the DOC, the blockage state being detected on the basis of comparison between a blockage parameter related to blockage of the DOC and a predetermined blockage threshold, the blockage risk state being detected when the diesel engine is in an operating state that is likely to cause blockage of the DOC; and b a DOC temperature increase execution part configured to execute a DOC temperature increase control including: a first temperature increase process to control the temperature increase unit, if the temperature increase necessary state of the DOC is detected, so as to increase a temperature of the DOC to a first temperature at which the DOC activates; and a second temperature increase process to control the temperature increase unit after completion of the first temperature increase process so as to increase the temperature of the DOC to a second temperature higher than the first temperature, wherein, during normal operation in which the forced regeneration process is not performed, the DOC temperature-increase-necessary-state detection part detects the blockage risk state of the DOC if an accumulated duration time, within a latest predetermined period, of a low exhaust temperature operation state exceeds a predetermined threshold, the low exhaust temperature operation state being a state where an exhaust gas temperature is lower than an exhaust temperature threshold. a DOC temperature-increase-necessary-state detection part configured to detect a temperature increase necessary state including at least one of a blockage state of the DOC or a blockage risk state of the DOC, the blockage state being detected on the basis of comparison between a blockage parameter related to blockage of the DOC and a predetermined blockage threshold, the blockage risk state being detected when the diesel engine is in an operating state that is likely to cause blockage of the DOC; and b a DOC temperature increase execution part configured to execute a DOC temperature increase control including: a first temperature increase process to control the temperature increase unit, if the temperature increase necessary state of the DOC is detected, so as to increase a temperature of the DOC to a first temperature at which the DOC activates; and a second temperature increase process to control the temperature increase unit after completion of the first temperature increase process so as to increase the temperature of the DOC to a second temperature higher than the first temperature, wherein, during normal operation in which the forced regeneration process is not performed, the DOC temperature-increase-necessary-state detection part detects the blockage risk state of the DOC if an accumulated duration time, within a latest predetermined period, of a low exhaust temperature operation state exceeds a predetermined threshold, the low exhaust temperature operation state being a state where an exhaust gas temperature is lower than an exhaust temperature threshold.