The invention aims to provide a novel alkaline protease having peculiar properties such as high alkali activity, resistance to surfactants and calcium-dependent thermostability and exhibiting excellent performance in highly alkaline detergents, and a gene coding for the amino acid sequence thereof. There is provided an alkaline protease with such properties that an active pH range is from 5 to 13, an optimum pH is approximately 12.6, an optimum temperature is 70° C., no activity drop by heating is observed up to 65° C. at pH 10 and the optimum temperature and the thermostability are not affected by Ca2+ ions. Specifically, there is provided, for example, an alkaline protease having an amino acid sequence constituting a mature enzyme as represented by SEQ ID NO: 3 or an amino acid sequence resulting from deletion, substitution, situs inversus arrangement, addition or insertion of a part of amino acids thereof, or derived from Alkaliphillus transvaalensis. The protease cleaves 26 peptide bonds among 29 peptide bonds of acidic insulin B-chain.