There is provided a two-port valve which has excellent durability and airtightness and can be easily processed with high accuracy and in which a valve seat can be easily replaced. For this purpose, a valve seat 8 is formed separately from a valve body 4 of a main valve and the valve body 4 is provided with a mounting portion 9 on which the valve seat 8 is seated. The mounting portion 9 is formed of an annular stepped portion including a bottom wall 41 and an outer peripheral wall 42. The bottom wall 41 is provided with a groove portion into which a sealant 44 is mounted and the outer peripheral wall 42 is provided in a vicinity of an upper portion thereof with a groove portion into which a snap ring 47 is mounted. The valve seat 8 is held pressed against the sealant 44 by the snap ring 47.