PURPOSE: To obtain the Σ modulator with high S/(N+D) when the level of an analog signal to be converted is low. (S is signal, H is noise, and D is distortion component)

CONSTITUTION: Two modulator is provided with an integration means 2 which integrates analog signal to be converted, a quantization means 3 which outputs the output signal of the means 2 by eight types of quantization compared with seven analog reference values VT1-VT7, an addition means 1 adding eight types of analog signal to the analog signal to be converted based on the output signal of the quantization means at the side of input of the means 2, and a means which makes high the ratio in space of eight types of analog signal value to be added to the analog signal to be converted for the quantization threshold value intervals in the means 3 as the absolute value of the output signal of the integration means 2 is high. Thus, when the level of the analog signal to be converted is low, the high S/(N+D) can be obtained.