'React' must be in scope when using JSX react/react-in-jsx-scope Error

When I ran the app, the above error occurred... I think that there is a conflict with eslint after installing Babel-plugin, but I don't know the exact solution.

<App.js>

import Header from '../src/components/Header'

function App() {
  return (
    <Header />
  );
};

export default App;

<Header.js>

import styled from 'styled-components'

const HeaderContainer = styled.div`

`;

function Header() {
    return (
        <HeaderContainer>Hello</HeaderContainer>
    )
};

export default Header;

FYI, adding "import React from 'react'" to Header.js doesn't change anything...