A wireless receiver which is used for a digital signal transmission system to wirelessly transmit a digital signal by packetizing and modifying it, selectively sets the shortest arithmetical bit length satisfying a required communication quality when performs demodulation arithmetical processing to demodulate a digital signal to be packet-transmitted, inputs a demodulation arithmetical result by the arithmetical bit length to calculate an error vector magnitude value that is a measure indicating a difference between the arithmetical result and a known ideal result, predicts a bit error rate by using the EVM value as an evaluation criterion, selects an arithmetical bit length by which the bit error rate becomes optimum, and executes the demodulating arithmetical processing by the selected arithmetical bit length.