Cryptography is core technology in information security field. Elliptic Curve Cryptosystem(ECC) can be constructed with small key size and is suitable in embedded systems. It is needed to protect side-channel attacks(SCA) when implementing cryptosystems. There are simple power analysis(SPA) with power consumption and safe error attack(SEA) with fault in SCA. This research aim is improving ECC algorithm with secure against SCA. Research object is Scalar multiplication because it is dominant in ECC. There are several previous works about improving it. Generally, there is a trade-off between amount of working memory and computation cost. In addition, coordinate systems should be selected depending on charactaristic of processor. In this work, we deal with arbiaty point, fixed point and multi scalar multiplication when used in signature verification. And performance indexes are amount of computation cost and working memory. We also improve scalar multiplication algorithm with using ROM.