An electrical conductivity detector includes a cell, a pair of electrodes, a voltage application part, an amplification circuit, a phase adjustment value holding part, and a signal processing circuit. The amplification circuit has multiple gains, and amplifies a current flowing between the pair of electrodes using any one of the gains to obtain an amplified signal. The phase adjustment value holding part holds a phase adjustment value determined in advance for each of the gains for canceling a phase difference between amplified signals determined using each of the gains of the amplification circuit. The signal processing circuit calculates electrical conductivity of the liquid flowing through the cell using an amplified signal obtained by being amplified by the amplification circuit and the phase adjustment value which is for the gain used to obtain the amplified signal and is held in the phase adjustment value holding part.