To provide a vaporizer prevented from a sudden pulsation caused by bubbles by preventing the generation of bubbles in liquid caused by heating.

The vaporizer has a first base plate 9 having grooves 11 formed on a surface at one side and a flow-in port 12 and a flow-out port 13 formed on both sides thereof; and a second base plate 14 having grooves 19 shaped same as the grooves 11 formed on the first base plate 9, formed on a surface facing the first base plate 9, and a thin film heater 17 arranged on a surface at the opposite side of the surface opposing the first base plate 9. A flow passage 21 is arranged on the groove 11 formed on the first base plate 9 and on the groove 19 formed on the second base plate 14 at the neighboring area of the flow-in port 12 which is a middle part of the grooves.