In an evaporated fuel treatment apparatus mounted laterally, in order to effectively utilize adsorbent of an upper portion in an adsorption chamber of the evaporated fuel treatment apparatus, the evaporated fuel treatment apparatus comprises: one or more adsorption chambers filled with the adsorbent that adsorbs and desorbs evaporated fuel generated in a fuel tank; a tank port; a purge port; and an atmosphere port, and in the evaporated fuel treatment apparatus, a first filter is provided in a boundary portion between the adsorption chamber located closest to the tank port and the tank port, and an amount of gas, having flowed in the adsorption chamber from the tank port, passing through an upper portion of the first filter is made larger than that of the gas passing through a lower portion thereof.