The paper concerns conception of law presented in Hobbes' 'Leviathan'. The author argues that for Hobbes the ultimate source of the binding force (normativity) of law is the sovereign's will, and reasons for that are 'technical'. The sovereign creates laws, because he is a representative of the state ('moral' or 'artificial' person) which is the real author of the law. However, the existence of the state is dependent on its members' will expressed in the social contract which Hobbes describes in terms of laws. The contract, however, needs background norms to bind its parties. Thus the social contract also cannot be the basis of normativity of the law, although it could be the cause of its being in force. Instead, the source of the binding force of the law is, in Hobbes' view, the law of nature. This law is unchangeable, eternal, autonomous, and rationally knowable.