A measuring apparatus (1, 2, 3) for contactlessly measuring vibration or displacement of a measurement target comprising: a light source configured to emit a continuous wave of light frequency-modulated to arrange a measurement site of the measurement target within a correlation peak; a divider (12, 21) configured to divide the continuous wave of light into first and second divided-waves of light; a light receiver configured to receive interfering light of the first divided-wave of light reflected by the measurement target and the second divided-wave of light; and a calculator configured to calculate the vibration or displacement of the measurement target using an electric signal output from the light receiver, wherein the light source has a modulation period and a modulation amplitude set to arrange the measurement site of the measurement target within the correlation peak, the correlation peak appears when an optical path difference between the first divided-wave of light and the second divided-wave of light is equal to zero or a value obtained by dividing the optical path difference by a light speed is an integral multiple of modulation period of the continuous wave of light, a peak of intensity of the electric signal indicates the correlation peak, wherein the modulation period and the modulation amplitude of the light source are set to arrange the measurement site of the measurement target at a former or a latter of the correlation peak having a mountain shape and the modulation period of the light source is set to an integral multiple of a value obtained by dividing a difference between a first length of a first optical path and a second length of a second optical path by a light speed or is set to a value close to the integral multiple, the first optical path leads the first divided-wave of light divided by the divider (12, 21) to the measurement target and leads the first divided-wave of light reflected by the measurement target to the light receiver, and the second optical path leads the second divided-wave of light divided by the divider (12, 21) to the light receiver. a light source configured to emit a continuous wave of light frequency-modulated to arrange a measurement site of the measurement target within a correlation peak; a divider (12, 21) configured to divide the continuous wave of light into first and second divided-waves of light; a light receiver configured to receive interfering light of the first divided-wave of light reflected by the measurement target and the second divided-wave of light; and a calculator configured to calculate the vibration or displacement of the measurement target using an electric signal output from the light receiver, wherein the light source has a modulation period and a modulation amplitude set to arrange the measurement site of the measurement target within the correlation peak, the correlation peak appears when an optical path difference between the first divided-wave of light and the second divided-wave of light is equal to zero or a value obtained by dividing the optical path difference by a light speed is an integral multiple of modulation period of the continuous wave of light, a peak of intensity of the electric signal indicates the correlation peak, wherein the modulation period and the modulation amplitude of the light source are set to arrange the measurement site of the measurement target at a former or a latter of the correlation peak having a mountain shape and the modulation period of the light source is set to an integral multiple of a value obtained by dividing a difference between a first length of a first optical path and a second length of a second optical path by a light speed or is set to a value close to the integral multiple, the first optical path leads the first divided-wave of light divided by the divider (12, 21) to the measurement target and leads the first divided-wave of light reflected by the measurement target to the light receiver, and the second optical path leads the second divided-wave of light divided by the divider (12, 21) to the light receiver.