Provided are a detector for a multi-level modulated signal and a detection method using the same, and an iterative receiver for a multi-level modulated signal and an iteratively receiving method using the same. The detector includes: a channel estimator estimating a channel response of each of a plurality of bits included in at least one received signal based on multi-level modulation; a hard decision unit, for each bit, selecting at least one of a plurality of bits remaining by excluding the bit and performing a hard decision based on a pre-probability of the selected bit; and a reliability calculator calculating reliability of each of all the bits in the received signal based on the received signal from which the hard-decided bit component is cancelled and the estimated channel response. Accordingly, the computation amount according to detection can be reduced without the degradation of performance.