An exhaust purification device for an internal combustion engine comprising a particulate filter for trapping particulate matter contained in exhaust gas and arranged in an engine exhaust passage, and a control unit, wherein: said particulate filter is provided with alternately arranged exhaust gas inflow passages and exhaust gas outflow passages and porous partition walls which separate these exhaust gas inflow passages and exhaust gas outflow passages from each other, micropore zones are defined at upstream sides of the partition walls in a longitudinal direction of the particulate filter, macropore zones are defined at downstream sides of the partition walls in the longitudinal direction of the particulate filter, a pore size of the partition walls in the micropore zones is set so that particulate matter and ash can be trapped by the partition walls at the micropore zones, a pore size of the partition walls in the macropore zones is set so that ash can pass through the partition walls at the macropore zones, the average pore size of the micropore zones is set to 10 μm to 25μm and the average pore size of the partition walls at the macropore zones is set to 25 μm to 100 μm, and the control unit is configured to increase gas which temporarily increases the flow rate of gas which flows into the particulate filter in order to remove the ash from the particulate filter, when a quantity of trapped particulate matter on the particulate filter is smaller than a predetermined limit quantity (QPMX), characterized in that: when said quantity of trapped particulate matter is smaller than said limit quantity (QPMX), said control unit is configured to not increase gas if an execution condition for control for increasing gas based on the engine operating conditions does not stand, but to increase gas when the execution condition stands. said particulate filter is provided with alternately arranged exhaust gas inflow passages and exhaust gas outflow passages and porous partition walls which separate these exhaust gas inflow passages and exhaust gas outflow passages from each other, micropore zones are defined at upstream sides of the partition walls in a longitudinal direction of the particulate filter, macropore zones are defined at downstream sides of the partition walls in the longitudinal direction of the particulate filter, a pore size of the partition walls in the micropore zones is set so that particulate matter and ash can be trapped by the partition walls at the micropore zones, a pore size of the partition walls in the macropore zones is set so that ash can pass through the partition walls at the macropore zones, the average pore size of the micropore zones is set to 10 μm to 25μm and the average pore size of the partition walls at the macropore zones is set to 25 μm to 100 μm, and the control unit is configured to increase gas which temporarily increases the flow rate of gas which flows into the particulate filter in order to remove the ash from the particulate filter, when a quantity of trapped particulate matter on the particulate filter is smaller than a predetermined limit quantity (QPMX), characterized in that: when said quantity of trapped particulate matter is smaller than said limit quantity (QPMX), said control unit is configured to not increase gas if an execution condition for control for increasing gas based on the engine operating conditions does not stand, but to increase gas when the execution condition stands.