A common tangent line drawn between a rise portion present from the origin to a second reference voltage and a rise portion corresponding to the second reference voltage can be easily generated through a waveform conversion. A transient recovery voltage measuring device includes a memory storing a transient recovery voltage waveform of a multiple frequency, a waveform conversion unit converting the transient recovery voltage waveform, a wave height determination unit determining two points having the same maximum value on the converted waveform, an adjustment unit adjusting the proportional constant of the waveform conversion unit to determine those two points by the wave height determination unit, a contact point detection unit obtaining two points corresponding to the determined two points determined by the wave height determination unit, and a tangent line generation unit generating a first tangent line passing through the detected two points on the transient recovery voltage waveform.