A photocurrent corresponding to the intensity of the light from the subject which photocurrent is successively generated at predetermined intervals is converted into a voltage by being logarithmically compressed by a logarithmic compression circuit in a divisional cell of a metering sensor during the preliminary light emission of the flash immediately before the actual shooting. Then, the voltage level is outputted to a controller as an analog metering signal. The controller A/D converts the successively inputted analog metering signal to generate digital data corresponding to the BV value representative of the brightness of the subject under flash light, and stores the digital data into a RAM. Then, the controller calculates a subject distance for determining the light emission amount of the flash in the actual shooting by performing a digital calculation including an integration calculation of the BV values obtained under ambient light and under flash light.