PROBLEM TO BE SOLVED: To provide a method for measuring a very small displacement of an object and its time change in non-contact and with high accuracy, a measuring device to which the method is applied, a displacement measuring device and a method for calculating a physiological index including a physiological parameter derived from the displacement of an organism measured by the device.SOLUTION: A displacement measuring method includes: a process of irradiating a first electromagnetic wave of a first frequency to an optional position, irradiating a second electromagnetic wave of a second frequency different from the first frequency to the above position, receiving scattered electromagnetic waves caused as the result of irradiating the first electromagnetic wave and the second electromagnetic wave, obtaining a phase difference &phgr(t) between a first difference output wave obtained by multiplication of the scattered electromagnetic wave and the first electromagnetic wave and a second difference output wave obtained by multiplication of the scattered electromagnetic wave and the second electromagnetic wave, and regarding the scattered electromagnetic wave as the first electromagnetic wave at the above position at a time T and the result of scattering of the first electromagnetic wave, defining a displacement &Dgrd(t) of the above position on the basis of the phase difference &phgr(t) and a difference &Dgr&phgr(t) of the phase difference &phgr(t), to calculate the displacement of the above position.
