An exhaust gas purification device comprising: a gas purification body (2, 3) which purifies exhaust gas discharged from an engine; a purification casing which accommodates the gas purification body; an exhaust gas inlet pipe which communicates with an exhaust gas inflow port of the purification casing; an exhaust gas outlet pipe which communicates with an exhaust gas outflow port of the purification casing; the exhaust gas inlet pipe being attached to the purification casing in such a manner as to cover the exhaust gas inflow port, characterized in that: the exhaust gas inlet pipe extends in a longitudinal direction of the purification casing; and an introduction passage of the exhaust gas is formed by an outside surface of the purification casing and an inside surface of a pipe wall of the exhaust gas inlet pipe, wherein: a portion extending along the purification casing in the pipe wall of the exhaust gas inlet pipe is inclined so as to come close to the outside surface of the purification casing gradually toward an exhaust gas outlet side from an exhaust gas inlet side of the exhaust gas inlet pipe; and a concave surface portion concaved outward is formed in an inner surface side of a side end surface close to the exhaust gas inflow port in the purification casing. a gas purification body (2, 3) which purifies exhaust gas discharged from an engine; a purification casing which accommodates the gas purification body; an exhaust gas inlet pipe which communicates with an exhaust gas inflow port of the purification casing; an exhaust gas outlet pipe which communicates with an exhaust gas outflow port of the purification casing; the exhaust gas inlet pipe being attached to the purification casing in such a manner as to cover the exhaust gas inflow port, characterized in that: the exhaust gas inlet pipe extends in a longitudinal direction of the purification casing; and an introduction passage of the exhaust gas is formed by an outside surface of the purification casing and an inside surface of a pipe wall of the exhaust gas inlet pipe, the exhaust gas inlet pipe extends in a longitudinal direction of the purification casing; and an introduction passage of the exhaust gas is formed by an outside surface of the purification casing and an inside surface of a pipe wall of the exhaust gas inlet pipe, wherein: a portion extending along the purification casing in the pipe wall of the exhaust gas inlet pipe is inclined so as to come close to the outside surface of the purification casing gradually toward an exhaust gas outlet side from an exhaust gas inlet side of the exhaust gas inlet pipe; and a concave surface portion concaved outward is formed in an inner surface side of a side end surface close to the exhaust gas inflow port in the purification casing. a portion extending along the purification casing in the pipe wall of the exhaust gas inlet pipe is inclined so as to come close to the outside surface of the purification casing gradually toward an exhaust gas outlet side from an exhaust gas inlet side of the exhaust gas inlet pipe; and a concave surface portion concaved outward is formed in an inner surface side of a side end surface close to the exhaust gas inflow port in the purification casing.