According to one embodiment, in an isolator, a first capacitive element is arranged on a first signal line. The first capacitive element has one end electrically connected to an input side circuit and having another end electrically connected to an output side circuit. A second capacitive element is arranged on a second signal line. The second capacitive element having one end electrically connected to the input side circuit and having another end electrically connected to the output side circuit. A first inductive element has one end electrically connected to a first node between the first capacitive element in the first signal line and the output side circuit. A second inductive element has one end electrically connected to a second node between the second capacitive element in the second signal line and the output side circuit.