The pair monitor measures the beam profile at the interaction point of the international linear collider. It extracts the information from the directional distribution of a large number of electron-positron pairs created by collision of bunches. The pairs are detected by pixel detectors placed close to the beam on both sides of the interaction point, and a readout ASIC that meets the stringent requirements has been developed. In order to measure the beam profile as a function of location within a train, and also to deal with the high hit rate, the pixel detector is read out in 16 time slices per bunch train. In this paper, we describe the design of the readout circuit and present the result of performance tests.