An image sensor has plural array blocks B1 to B20 arranged in a two dimensional (2D) arrangement. Each array block has a sub array and a corresponding analogue to digital (A/D) converter for performing an A/D conversion of light signals (or detection signals) output from the sub array. The sub array has plural picture element cells arranged in a 2D arrangement. Each A/D converter has a pulse delay circuit having delay units of plural stages connected in series. Each delay unit delays an input pulse by a delay time corresponding to a level of the light signals received from the sub array. A pulse delay type A/D converter is used as the A/D converter, which outputs the number of the delay units as an A/D conversion data item through which the input pulse passes for a measurement time period.