A demodulation unit for a GNSS signal processing device includes an operator that uses a first error detecting method when one of a first selection criterion in which an early late differential value is higher than a first threshold (positive value) and an early differential value is lower than a third threshold (negative value), and a second selection criterion in which the early late differential value is lower than a second threshold (negative value) and a late differential value is lower than a fourth threshold (negative value) is satisfied, and the operator uses a second error detecting method when neither criterion is satisfied. A code phase range where an error detection value is not 0 is wide with the first error detecting method, and the code phase range where the error detection value is not 0 is narrow with the second error detecting method.