A vibration isolator in which a portion of a wall surface in at least one of the group consisting of a first liquid chamber and a second liquid chamber is formed using an elastic body, the vibration isolator comprising: a first tubular attachment member coupled to one of the group consisting of a vibration generating part and a vibration receiving part; a second attachment member coupled to the other of the vibration generating part and the vibration receiving part; the elastic body configured to couple together the first attachment member and the second attachment member; and a partition member configured to partition a liquid chamber in the first attachment member in which a liquid is sealed into the first liquid chamber and the second liquid chamber, wherein a communicating passage configured to communicate the first liquid chamber with the second liquid chamber is provided in the partition member, a flow changing protrusion protruding from an inner circumferential surface of the communicating passage and configured to change a flow of the liquid flowing in the communicating passage in its axial direction is provided at the inner circumferential surface thereof; a guide surface facing the communicating passage and intersecting the axial direction is provided at the flow changing protrusion; a passing hole which is open toward both sides in the axial direction is formed by a projecting end of the flow changing protrusion and another place on the inner circumferential surface of the communicating passage; the flow changing protrusion is configured to change a flow of the liquid flowing in the communicating passage and reaching the guide surface toward the projecting end and is integrally formed with the partition member using a resin material, as a rigid body having a rigidity that prevents it from being remarkably deformed when receiving the flow of the liquid; the guide surface is formed in a concave curved surface shape which is recessed in the axial direction; and wherein the vibration isolator comprises at least one of said flow changing protrusion, such that guide surfaces are provided at both end surfaces of said flow changing protrusion in the axis direction of the communication passage, or wherein the vibration isolator comprises at least one pair of flow changing protrusions, such that for each pair of flow changing protrusions a guide surface is provided at one of the flow changing protrusion and faces a first side in the axial direction of the communicating passage and another guide surface is provided at the other of the flow changing protrusions and faces a second side in the axial direction of the communicating passage. a first tubular attachment member coupled to one of the group consisting of a vibration generating part and a vibration receiving part; a second attachment member coupled to the other of the vibration generating part and the vibration receiving part; the elastic body configured to couple together the first attachment member and the second attachment member; and a partition member configured to partition a liquid chamber in the first attachment member in which a liquid is sealed into the first liquid chamber and the second liquid chamber, wherein a communicating passage configured to communicate the first liquid chamber with the second liquid chamber is provided in the partition member, a flow changing protrusion protruding from an inner circumferential surface of the communicating passage and configured to change a flow of the liquid flowing in the communicating passage in its axial direction is provided at the inner circumferential surface thereof; a guide surface facing the communicating passage and intersecting the axial direction is provided at the flow changing protrusion; a passing hole which is open toward both sides in the axial direction is formed by a projecting end of the flow changing protrusion and another place on the inner circumferential surface of the communicating passage; the flow changing protrusion is configured to change a flow of the liquid flowing in the communicating passage and reaching the guide surface toward the projecting end and is integrally formed with the partition member using a resin material, as a rigid body having a rigidity that prevents it from being remarkably deformed when receiving the flow of the liquid; the guide surface is formed in a concave curved surface shape which is recessed in the axial direction; and wherein the vibration isolator comprises at least one of said flow changing protrusion, such that guide surfaces are provided at both end surfaces of said flow changing protrusion in the axis direction of the communication passage, or