PURPOSE: To measure a high speed electric signal even not in the case of a repetitive signal by extracting a charge at each point at a storage means with one ultrashort pulse light radiation by plural high speed optical operating switch means arranged along a transmission line and measuring plural points simultaneously a voltage in a prescribed timing of an electric signal to be measured propagated through the transmission line.

CONSTITUTION: An electric signal to be measured inputted from an input terminal 13 to a transmission line 12 is sent at a transmission speed depending on the characteristic of the transmission line 12. While the electric signal to be measured is being sent to the transmission line 12, a light radiation means 20 use an ultrashort pulse light which irradiates optical operating switches 14A - 14L simultaneously synchronously with the transmission. Thus, the charge in the vicinity of the connection point between the optical operating switches 14A - 14L and the transmission line 12 is sent to storage means 16A - 16L connected to the optical operating switches 14A - 14L respectively. The quantity of charge stored in the storage means 16A - 16L is read by a read means 18. Thus, in the case of a high speed electric signal, an event that only a repetitive electric signal can be used for the measurement is avoided.