This paper presents the size-reduced branch-line power divider using shunt-stub. By the equivalent circuits of quarter wavelength transmission line, each line of the branch-line divider is defined as the specific impedance value and the electric length of shunt-stub is given as a function of impedance of shunt-stub. It is shown that the bandwidth of the divider is decreased with decreasing size and/or increasing electric length of the shunt-stub. In spite of narrow band, these size-reduced branch-line power dividers using shunt-stub can be applied to a wireless-LAN system.