The exhaust gas purification device includes an exhaust gas post-processing device 30 provided in an exhaust passage 11 of an engine 10, an exhaust injection valve 22, a first catalyst 35, a second catalyst 36 for thermally decomposing fuel injected by the exhaust injection valve 22, an exhaust temperature estimation unit 41 for estimating an exhaust temperature, an engine injection control unit 42 for controlling fuel injection in the engine 10, and regeneration control units 43, 44 for controlling regeneration of the exhaust gas post-processing device 30. When an output value output by the exhaust gas temperature estimation unit 41 is equal to or lower than a threshold during regeneration by the regeneration control units 43, 44, the engine injection control unit 42 controls fuel injection in the engine by performing a multistage injection, which includes a post injection for supplying fuel to the first catalyst 35.