Provided is a wet exhaust gas purification device capable of removing deposited particulate matter from the demister and using demisters with an open ratio for collecting particulate matter efficiently. The device uses means for heating the demister to a temperature (60°C) at which the deposited oily particulate matter exhibits a lower viscosity or a temperature (600°C or more) at which the particulate matter burns spontaneously. This results in that the oily particulate matter as it is softened and liquified to the extent that it can drop under its own weight is easily washed away from the demister or the burned particulate matter residuals are washed away completely, which ensures to remove the particulate matter in a short period of time and with a minimum amount of cleaning water. The demister from which the particulate matter has been washed away can be renewed as new one.