The Jagiellonian Positron Emission Tomograph (J-PET) project carried out in the Institute of Physics of the Jagiellonian University is focused on construction and tests of the first prototype of PET scanner for medical diagnostic which allows for the simultaneous 3D imaging of the whole human body using organic scintillators. The J-PET prototype consists of 192 scintillator strips forming three cylindrical layers which are optimized for the detection of photons from the electron-positron annihilation with high time- and high angular-resolutions. In this article we present time calibration and synchronization of the whole J-PET detection system by irradiating each single detection module with a 22Na source and a small detector providing common reference time for synchronization of all the modules.