A strong external magnetic field, Hc=176 kOe, applied along the ordering axis of antiferromagnetic NiWO4produces spin flopping. This orientational transition results in sharp changes both in longitudinal and transverse components of the magnetization vector. It is found that for certain external magnetic field orientations, spin flopping in NiWO4is a first order phase transition. The measurement results for magnetic properties suggest that an intermediate state appears in this field region, where the sample laminates into magnetic domains. The domain layer directions make an angle with the vector of the inducing magnetic field, which can be varied by minor changes in the external field direction.