To provide a visual field expansion device capable of being easily installed for stereoscopically observing an article in a position lying on one's back.

A second mirror panel 2 is freely bendably connected to one side edge of a first mirror panel 1, a third mirror panel 3 is freely bendably connected to one end edge of the first mirror panel 1 and a fourth mirror panel 4 is freely bendably connected to the other end edge of the second mirror panel 2. Then, a supporting rod 6 is connected to a frame 5 fixed to the peripheral edge of the second mirror panel 2, the supporting rod 6 is attached to the frame F of a bed B, the angles of the mirror panels 1, 2, 3 and 4 are appropriately adjusted opposing the head part of a person H lying on his/her back and the article mounted on a mounting base D is reflected and observed.