This paper proposes a compact hardware (H/W) implementation for the MISTY1 block cipher, which is one of the ISO/IEC 18033-3 standard encryption algorithms. In designing the compact H/W, we focused on optimizing the implementation of FO/FI/FL functions, which are the main components of MISTY1. For this optimization, we propose three new methods; reducing temporary registers for the FO function, shortening the critical path for the FI function, and merging the FL/FL^-1 functions. According to our logic synthesis on a 0.18-µm CMOS standard cell library based on our proposed methods, the gate size is 3.4Kgates, which is the smallest as far as we know.