A solid state image pickup apparatus includes a solid state image pickup device for receiving an optical image of an object and generating an electrical image signal representing the optical image of the object in synchronism with a driving pulse from a driving circuit. A sampling circuit generates a sampled image signal by sampling the electrical image signal read out of the solid state image pickup device with a first sampling pulse from a first pulse circuit synchronized with the driving pulse. An analog-to-digital convertor converts the sampled image signal to a digital image signal with a second sampling pulse from a second pulse circuit. A test signal generator generates a test signal which is synchronized with the driving pulse and alternately changes in level between consecutive pixels. A controller controls the phase of the first sampling pulse and the phase of the second sampling pulse relative to each other by processing the test signal.