We investigated the shear-induced phase separation and/or concentration fluctuation phenomena in semidilute polymer solution by using computer simulation in 3-dimensional space with Doi-Onuki theory. The enhancement of the concentration fluctuations occurs under shear flow and the scattering function in q(x)-q(Sigma) plane exhibits the so-called butterfly pattern as observed experimentally, where q(x) and q(z) are the components of the scattering vector for flow direction and neutral direction, respectively. The time changes in the peak position and the intensity at peak position in the scattering function in q(x)-q(z) plane can be divided into two regions: the peak position becomes smaller and the peak intensity increases with t, and then the peak position and intensity become constant and the system reaches its steady state. These agree with the experimental results qualitatively. However, the computer simulation results indicate that the peak position at the steady state is almost independent of the shear rate, while the decrease in the peak position at steady state with shear rate has been observed experimentally. This disagreement originates from the use of the simplest constitutive equation in the computer simulation. (c) 2006 Elsevier Ltd. All rights reserved.