  This contribution is devoted to the study of positional numeration systems
with negative base introduced by Ito and Sadahiro in 2009, called
(-\beta)-expansions. We give an admissibility criterion for more general case
of (-\beta)-expansions and discuss the properties of the set of
(-\beta)-integers. We give a description of distances within this set and show
that this set can be coded by an infinite word over an infinite alphabet, which
is a fixed point of a non-erasing non-trivial morphism.
