The present invention provides a steam injection mechanism improved so that water accumulation on an object to be processed can be reliably restricted. A steam injection mechanism 3 comprises a common channel 31 through which steam supplied from a steam supply source flows and distribution channels 32 branched from the common channel 31 to distribute the steam from the common channel 31 wherein the steam is injected from steam injection orifices 32d formed in distal ends of the distribution channels 32 to an object 100 (a fibrous nonwoven fabric) to be processed. When the steam injection mechanism 3 is located above the fibrous nonwoven fabric, the lowermost region 31d of the common channel 31 functions as a condensed water collecting region and, when the steam injection mechanism 3 is located under the fibrous nonwoven fabric, the uppermost region 31u of the common channel 31 functions as the condensed water collecting region.