An exhaust gas purification device comprising: a catalyst provided downstream of an enlarged diameter flow path in an exhaust gas flow path; a diffusion member provided upstream of the enlarged diameter flow path in the exhaust gas flow path, the diffusion member configured to cause exhaust gas that has flowed in from upstream to flow out to the enlarged diameter flow path to be diffused; a supply device for supplying a reducing agent to upstream of the diffusion member in the exhaust gas flow path; a guide member (10, 20, 30, 40, 50, 60) provided upstream of the diffusion member, and at a merging position, or downstream of the merging position, where the reducing agent in the exhaust gas flow path merges with the exhaust gas, the guide member configured to split a flow of the reducing agent that has flowed in from upstream into a plurality of flows to guide the flows to the diffusion member, wherein the guide member comprises a plate (11, 12, 13, 21, 22, 31, 32, 33, 41, 42, 43, 51, 52, 53) with an air guide (11A, 12A, 13A, 21A, 22A, 31A, 32A, 33A, 41A, 42A, 43A, 51A, 52A, 53A) that is a protruding piece extending toward the merging position, the air guide configured to split the flow of the reducing agent to a first surface side of the plate, and to a second surface side that is a back surface of the first surface, the plate comprises: a first plate (11, 21, 31, 41, 51); and a second plate (12, 22, 32, 42, 52), the first plate and the second plate are configured such that the second surface of the first plate and the first surface of the second plate face each other at a distance, characterized in that the first plate is provided upstream of the second plate in the exhaust gas flow path, and the air guide formed in the second plate is configured such that a width in a direction orthogonal to a direction in which the reducing agent flows is formed wider than that of the air guide formed in the first plate. a catalyst provided downstream of an enlarged diameter flow path in an exhaust gas flow path; a diffusion member provided upstream of the enlarged diameter flow path in the exhaust gas flow path, the diffusion member configured to cause exhaust gas that has flowed in from upstream to flow out to the enlarged diameter flow path to be diffused; a supply device for supplying a reducing agent to upstream of the diffusion member in the exhaust gas flow path; a guide member (10, 20, 30, 40, 50, 60) provided upstream of the diffusion member, and at a merging position, or downstream of the merging position, where the reducing agent in the exhaust gas flow path merges with the exhaust gas, the guide member configured to split a flow of the reducing agent that has flowed in from upstream into a plurality of flows to guide the flows to the diffusion member, wherein the guide member comprises a plate (11, 12, 13, 21, 22, 31, 32, 33, 41, 42, 43, 51, 52, 53) with an air guide (11A, 12A, 13A, 21A, 22A, 31A, 32A, 33A, 41A, 42A, 43A, 51A, 52A, 53A) that is a protruding piece extending toward the merging position, the air guide configured to split the flow of the reducing agent to a first surface side of the plate, and to a second surface side that is a back surface of the first surface, the plate comprises: a first plate (11, 21, 31, 41, 51); and a second plate (12, 22, 32, 42, 52), a first plate (11, 21, 31, 41, 51); and a second plate (12, 22, 32, 42, 52), the first plate and the second plate are configured such that the second surface of the first plate and the first surface of the second plate face each other at a distance, characterized in that the first plate is provided upstream of the second plate in the exhaust gas flow path, and the air guide formed in the second plate is configured such that a width in a direction orthogonal to a direction in which the reducing agent flows is formed wider than that of the air guide formed in the first plate.