A separation membrane module (1) includes: a monolith type reactor (1); a housing (3); an annular first sealing portion (4) sealing a gap between the housing (3) and a first end portion (1a) of the reactor; and an annular second sealing portion (5) sealing a gap between the housing (3) and a second end portion (1b) of the reactor. The first sealing portion (4) is deformable or movable in a longitudinal direction together with the reactor (1). The second sealing portion (5) fixes the reactor (1) to the housing (5).