Producing method of laminated filter

A producing method of a laminated filter wherein a corrugation forming apparatus sandwiches a plurality of filter media, the plurality of filter media including a first filter medium and a second filter medium, the first filter medium having a first thermoplastic resin including first constituent fibers and having a first melting temperature, and the second filter medium having a second thermoplastic resin including second constituent fibers and having a second melting temperature less than the first melting temperature,

• in a state in which the filter media are superposed on each other, the corrugation forming apparatus heats and presses the filter media at a softening temperature equal to or lower than the second melting temperature, the pressing being carried out such that the pressing of the second filter medium against the first filter medium crushes a weaving structure of the first fiber medium, the pressing further causes the second constituent fibers to become entangled with the first constituent fibers without closing gaps between the first constituent fibers, thereby corrugation-forming the filter media, and the filter media are thermally adhered to each other, and
• the thermally adhered filter media are frilly folded in a zigzag manner, and the corrugation formation in a concave and convex shape on a surface of the frilly folded filter media extends in a direction intersecting at right angle with a ridgeline direction of the frilly folded filter media.