We have attempted to synthesize diamonds on substrates using the simple hot-filament-assisted chemical vapour deposition (CVD) system reported by Hirose et al. (42nd Spring Meeting of Japan Society of Applied Physics and Related Societies, 1995, Extended Abstract, p. 374), Diamonds are synthesized, close to atmospheric pressure, from methanol without hydrogen gas in Hirose’s CVD system. In this paper, we report the dependence of crystal growth on the bias voltage and distance between the filament and the substrate. No crystal growth can be observed for synthesis with a negative bias voltage. Different stages of crystal growth, which seem to occur due to the temperature gradient on the substrate, are observed on the same substrate for synthesis with a large distance between the filament and the substrate.