A Scanning SQUID Microscope (SSM), developed by using our own Nb–AlOx–Nb technology, is used to study the distribution of vortices in a superconducting thin film and their movements induced by applied current. The SQUID sensor is a first-order gradiometer with an overall equivalent flux noise of about 5×10-6Φ0Hz-1/2. Using this SSM system, we obtain the vortex images before and after a pulse current with a variable amplitude and duration time is applied to the sample. The changes of a series of vortex images with increasing amplitude of the current pulse provide us with an estimate of the vortex pinning force at various pinning sites and their distribution.