Steady-state visually evoked potentials/fields (SSVEPs/SSVEFs) has been shown to be useful for many paradigms in cognitive (visual attention, working memory, and brain rhythms) and clinical neuroscience (aging, stress, and neurodegenerative disorders). The aim of this study was to examine the SSVEFs associated with the processing of positive and negative impression images. We used the International Affective Picture System (IAPS) which is increasingly used in brain imaging studies to examine emotional processes. Their images also allow valence to be systematically investigated. Seventy-five IAPS images of positive, neutral and negative valence assessed by subjects prior to the magnetoencephalogram (MEG) measurement were used. The peripheral square, i. e., frame, of the image was flickered black and white at 15 Hz while the image was kept stationary. Those images were randomly presented for 2.0 s on screen set at 120 cm in front of the subject. Ten healthy subjects participated. MEG recordings were made with a 122-channel whole-head MEG system in a magnetically shielded room. The MEG signals were bandpass filtered from 0.03 to 100 Hz and sampled at 1000 Hz. At least 50 epochs were recorded for averaging. We made multi-dipole estimation of the averaged MEG signals and obtained the amplitude of souse waveform in 15 Hz component (using a bandpass filter at 14-16 Hz) of SSVEF in occipital area. The amplitude of the SSVEF source in the occipital area was larger in the negative impression images than the positive impression images (p < 0.05). This result suggests that the amplitude of SSVEF that originated from the surrounding field of visual object was modulated by the emotional object and that the SSVEF could be a measure of emotion of subjects.