of the has a size fallen within a range from dozens u03bcm square or u03c6 to a few hundred u03bcm square or u03c6 the interterminal capacity is less than 1 pf and the response speed that is more than a few mhz can be realized when the photodiode is other type photodiode for example an avalanche photodiode the response speed may be further improved in general the maximum response speed is a few 100 khz in the world of displacement meter according to the second embodiment a displacement meter having a response speed of more than 1 mhz which is the fastest in the history of displacement meter can be realized since the fast measurement that is not available through the conventional devices is realized an evaluation of high speed response of mens actuator an ultrahigh throughput of three dimensional shape measurement and a real time testing of a high speed rotating body for example a turbine which is unnecessary to reduce the high speed rotating body for the testing can be realized besides concave mirrors 64 a and 64 b shown in fig1 can be used to replace the lenses 62 a and 62 b when the lenses 62 a and 62 b shown in fig1 b or the concave mirrors 64 a and 64 b shown in fig1 are used the amount of light received at the light receiving elements 58 a and 58 b can be ensured further if the amount of light received.