The objective of the present invention is to provide a heat exchanger having a configuration and structure capable of efficiently heating fluid inside a fluid flow path. In the present invention, a substantially S-shaped loop (SLTE) is formed at a substantial central part (C) and a substantially helical winding tube (STE) is formed at an outer periphery of the loop (SLTE). A fluid inlet (12) and a fluid outlet (13) are arranged along a direction substantially similar to or substantially opposite to a side part (S). The loop (SLTE), the winding tube (STE), the fluid inlet (12) and the fluid outlet (13) are substantially arranged on the same plane. A cross-section of the winding tube (STE) is formed into a substantially elliptical shape. A flat rate of the substantially elliptical shape is within a range of 30% to 70%. Each tube (T) that constitutes the winding tube (STE) is fixed at the adjacent side part (S) with thermal welding.本發明的課題，在於提供具有可效率佳地對流體流路內部的液體進行加溫的形狀和結構的熱交換器。本發明係於大致中心部(C)形成大致S字狀的回路(SLTE)，並在該回路(SL)的外周形成大致螺旋狀的捲繞管(STE)。液體流入口(12)和液體流出口(13)朝向大致相同或大致相反的側部(S)的一個方向而配置，上述回路(SLTE)、上述捲繞管(STE)、上述液體流入口(12)以及上述液體流出口(13)配置於實質上相同的平面上。上述捲繞管(STE)的截面形成為大致橢圓狀，該大致橢圓的扁平率在30至70%的範圍內。構成上述捲繞管(STE)的各管(T)相鄰接的側部(S)係藉由熱熔接而固定。
