This paper describes a new extrinsic calibration method to estimate the extrinsic parameters of a multi layer laser scanner relative to a stereo camera. Unlike the existing methods, this method has two main advantages: it is automatic and single stepped. The user imprecise selections of calibration features are avoided by using the features of a special designed object as calibration features. The extraction and matching of calibration object features are accurate and automatic. Non coplanar distribution of calibration object features introduces strong constraints on extrinsic parameters. By using these constraints the computation of extrinsic parameters is simultaneously done in a single step. In addition the assumptions on extrinsic parameters and error minimization steps required by existing methods are avoided. The proposed method is tested and the obtained results prove its accuracy.