PURPOSE: To make circuit constitution simple by counting shutter speed by an approximate formula at the time of reproducing the digitized shutter speed signal to the actual time.

CONSTITUTION: When the shortest exposure time is let to be Tst, the contents of the integer parts of shutter speed T to be 2n and the contents of the decimal part to be 2b/a, T=Tst.2n.2b/a is approximated to T=Tst.2n(1+b/a)=Tst.2n+ (Tst/2).2n.b and is counted 2n times by the pulse number of the Tst which becomes a reference time. T is reproduced by utilizing this count time. Namely, when the decimal part of the T does not exist, the shutter closing signal is formed when a binary counter C counts 2n pulses. When the decimal part of the T exists, the pulses are counted 2n×b times by the frequency of Tst/a and the shutter closing signal is formed after the time being the sum of the above count time and this count time.