To provide an insulator that can reduce an abnormal noise made when stopper surfaces abut and separate. A first mounting hole engaging a vehicle body side is formed in a first portion. A second mounting hole is formed in a second portion and arranged separately from the first portion. The first portion and the second portion form a first stopper surface and a second stopper surface, respectively. At least one of the first stopper surface and the second stopper surface opposite to one another is formed in a curved surface shape as a part of a cylindrical side surface. The first stopper surface and the second stopper surface can have a non-linear property when abutting and separating. Accordingly, an abnormal noise made when abutting and separating can be reduced.