A first detection unit and a second detection unit detect the light that is incident from the direction where a screen is to be located. A controller determines whether the screen is located at a recommended position based on output signals from the first detection unit and the second detection unit. When the screen is located at the recommended position, the controller controls the projection display apparatus so as to be in the state where a significant image can be projected. The controller may determine whether the screen is located at the recommended position and in a normal state based on the output signals. When the screen is located at the recommended position and in a normal state, the controller may control the projection display apparatus so as to be in the state where a significant image can be projected.