A check valve (1) includes a casing (2) having a valve seat (10) formed in a flow path and a valving element assembly (21) disposed in the casing. A top (23) of a valving element (22) is received in a large-diameter portion (38) of a through-hole (37) in a support member (35) of the valving element assembly. A narrow flow path portion (68) is formed between an arcuate portion (46) of an outer periphery (45) of the support member and a second enlarged-diameter portion (11) of the casing. The narrow flow path portion (a first portion of an intermediate flow path) is communicated with a back-pressure chamber (50) defined in the support member at the rear of the top of the valving element through a communicating passage (67) including a gap (66) between the outer periphery of the valving element and the inner periphery of the large-diameter portion and grooves (27) on the rear surface of the top of the valving element. A low static pressure of fluid flowing through the narrow flow path portion is introduced into the back-pressure chamber. Fluid passing through the narrow flow path portion enters a diffuser flow path portion (69) as a second portion of the intermediate flow path and recovers the static pressure while flowing therethrough. Next, the fluid flows downstream through a uniform flow path portion as a third portion of the intermediate flow path while maintaining the recovered static pressure.