  We discuss a model nonfrustrated magnetoelectric in which strong enough
magnetoelectric coupling produces incommensurate magnetic order leading to
ferroelectricity. Properties of the magnetoelectric in magnetic field directed
perpendicular to wave vector describing the spin helix are considered in
detail. Analysis of classical energy shows that in contrast to naive
expectation the onset of ferroelectricity takes place at a field $H_{c1}$ that
is lower than the saturation field $H_{c2}$. One has $H_{c1}=H_{c2}$ at strong
enough magnetoelectric coupling. We show that at H=0 the ferroelectricity
appears at $T=T_{FE}<T_N$. Qualitative discussion of phase diagram in $H-T$
plane is presented within mean field approach.
