A fastener device is disclosed, which comprises an inserting part, a socket having an insertion aperture and an intermediate filament connecting the inserting part and the socket. The inserting part, which can be inserted into the socket from either of two insertion directions of the aperture, has at least one tongue, which has a suitable elasticity and can expand in radial directions relative to the axis of the inserting part under its condition free of any force application. The aperture of the socket has a face to engage and stop the socket, which is vertically provided relative to the axis of the aperture. In inserting the inserting part into the socket, the tongue undergoes contraction to facilitate its passage through the aperture, and when it has been completely passed through the aperture, the tongue restores its original condition and radially expands to abut against the engaging face of the aperture, preventing the inserting portion from being pulled out of the socket. This fastener device is formed from a synthetic resin in an integral structure.