1. An interference reduction receiving device demodulating a signal by despreading a digital signal at a plurality of timings, by multiplying each of signals after being despread by a weight corresponding to each of the plurality of timings at which to perform despreading, and by combining the signals, the interference reduction receiving device comprising: an estimation unit estimating, based on the digital signal, a channel response vector having, as elements, channel estimation values corresponding to each of the plurality of timings; a quantizing unit quantizing the digital signal in the vicinity of each of the plurality of timings; a delaying unit delaying each of the quantized signals by a time difference between the timing corresponding to each of the quantized signals and another timing in the plurality of timings; a signal correlation matrix generation unit generating a signal correlation matrix having, as the element, each of signal correlation values calculated based on each of the quantized signals and on each of the delay signals that has been delayed by the delaying unit; and an weight calculating unit calculating each of the weights corresponding to each of the plurality of timings based on the channel response vector and the signal correlation matrix.