A method for increasing a thickness of a non-woven fabric, wherein said method comprises the steps of: feeding a web of non-woven fabric in a machine direction, wherein said non-woven fabric of a mass of thermoplastic synthetic fibers entangled one with another and having a transverse direction, a longitudinal direction and a thickness direction being orthogonal one to another and upper and lower surfaces (1a, 1b) opposite to each other in said thickness direction and extending in said transverse direction as well as in said longitudinal direction; and applying first jet streams of hot gas in said thickness direction to said web of non-woven fabric in a course of being fed in said machine direction to increase said thickness of said non-woven fabric, said method being characterized in that: a temperature of said first jet streams of hot gas is lower than a temperature at which thermoplastics forming a surface of said thermoplastic synthetic fibers begins to melt; and said step of applying said first jet streams of hot gas further comprises secondary steps of: heating said non-woven fabric by applying said first jet streams of hot gas on one surface of said upper and lower surfaces of said non-woven fabric in a single direction so that said first streams of hot gas penetrate fiber interstices formed of said mass of thermoplastic synthetic fibers; and striking said first jet streams of hot gas against a means adapted to divert pathways of said first jet streams of hot gas to reflect said first jet streams of hot gas and make said first jet streams of hot gas heat said non-woven fabric further and thereby to increase said thickness of said non-woven fabric, characterized in that said means used to divert said pathways of said first jet streams of hot gas comprises one of an air-impervious fixed plate slidably supporting said web of said non-woven fabric from said lower surface thereof in said machine direction, an air-impervious belt being movable in said machine direction together with said web of non-woven fabric supported thereon and an air-impervious peripheral surface of a roll adapted to rotate in said machine direction. a temperature of said first jet streams of hot gas is lower than a temperature at which thermoplastics forming a surface of said thermoplastic synthetic fibers begins to melt; and said step of applying said first jet streams of hot gas further comprises secondary steps of: heating said non-woven fabric by applying said first jet streams of hot gas on one surface of said upper and lower surfaces of said non-woven fabric in a single direction so that said first streams of hot gas penetrate fiber interstices formed of said mass of thermoplastic synthetic fibers; and striking said first jet streams of hot gas against a means adapted to divert pathways of said first jet streams of hot gas to reflect said first jet streams of hot gas and make said first jet streams of hot gas heat said non-woven fabric further and thereby to increase said thickness of said non-woven fabric, characterized in that said means used to divert said pathways of said first jet streams of hot gas comprises one of an air-impervious fixed plate slidably supporting said web of said non-woven fabric from said lower surface thereof in said machine direction, an air-impervious belt being movable in said machine direction together with said web of non-woven fabric supported thereon and an air-impervious peripheral surface of a roll adapted to rotate in said machine direction.