To solve a problem of damaging a claw member when fitting a male joint to a female joint because of failing to impart flexibility to the claw member provided at the male joint in the case of trying to simplify structure using hard synthetic resin in composing a one-way joint for connecting concrete blocks, of the male joint and female joint connected to each other by male-female engagement.

The one-way joint has the male joint and the female joint connected to each other by male-female engagement. The male member is provided with a shaft part extending in a proceeding direction, and a hook part projected sideways from the shaft part, while the female member is provided with a guide hole positioned in front in the proceeding direction of the male member, and the claw member obliquely extending in the proceeding direction into an admission passage of the male member from the edge part of the guide hole. The female member and the claw member are formed of hard synthetic resin, and both members are connected by a spring member formed of flexible soft synthetic resin.