Injection of a squeezed vacuum into a gravitational-wave detector is a way to improve its shot-noise limited sensitivity without increasing the laser power. The squeezer is placed outside the detector and decreases the vacuum fluctuation in the phase quadrature. Here we propose a new scheme to utilize the squeezer. The squeezer is placed inside a cavity and decreases the vacuum fluctuation in the phase quadrature just slightly so as to realize the impedance matching, with which the shot-noise limited sensitivity can be improved much better than the conventional scheme with the squeezer outside the detector.