A blood flow index calculating method includes: obtaining, by a camera, an image capturing a first site of a living body and a second site of the living body; extracting an area of the first site of the living body and an area of the second site of the living body, by a processor; detecting a pulse wave pattern of the first site of the living body from the area of the first site of the living body and detecting a pulse wave pattern of the second site of the living body from the area of the second site of the living body, by the processor; first calculating a delay amount from the pulse wave pattern of the first site and the pulse wave pattern of the second site, by the processor; and second calculating an index related to blood flow by using the delay amount, by the processor.