Abstract: A liquid-sealing type vibration-isolating device has a primary fluid chamber and a subsidiary fluid chamber which communicate with each other through a short idle orifice and a long shock orifice, and a switch-over valve for connecting the primary and subsidiary fluid chambers with each other through the idle orifice in the low speed revolution range of an engine mounted on the device and through the long shock orifice in the medium-high speed revolution range. During the shifting of the switch-over valve, in order to prevent sudden increase in the spring constant of the device, the primary fluid is short-circuited with the subsidiary fluid chamber through a communication port, the inside of a valve member, a communication bore and an auxiliary communication passage.