Microstereolithography (MSTL) is a SFF technology that has been used to fabricate 3-D scaffolds in tissue engineering. Projection-based microstereolithography (pMSTL) offers the advantage of increased fabrication speed compared with a line-scan-based MSTL by creating 2-D patterns with single-section image exposure and then stacking them. To fabricate a complex 3-D structure for a target tissue (liver, blood vessel, etc.) using the pMSTL system, we introduce a new algorithm that automatically generates projection image information. The procedure uses the STL file format as the raw data for a 3-D model. First, the STL file data are converted into slicing data composed of closed loops, including layer thicknesses. Projection image data are then generated from the closed loops calculated during the slicing process. Finally, the projection image data are converted into pixel information. The proposed technique is evaluated by fabricating a complex 3-D vascular network structure, and is shown to be quite practical for automated fabrication of complex 3-D structures in tissue engineering.