Deposition of diamond-like carbon (DLC) film and mass spectrometry measurements were carried out in a closed-space CH4 rf (13.56 MHz) plasma (without both gas injection and vacuum pumping during the process). At pressures less than 0.6 Torr, the thickness of the DLC film deposited increased with increasing elapsed deposition time, and reached a maximum value, but after this the film thickness started to decrease, which was considered to be caused predominantly by ion-induced sputter etching. The maximum film thickness appeared at larger elapsed time for higher deposition pressure. The mass concentrations of hydrocarbon ions indicated anomalous behavior at early deposition times, but those of higher hydrocarbon ions are clearly increased at the point where the film thickness started to decrease. These results suggested that the ratio of precursor CH radical density to the total hydrocarbon ion density (Phi(CH3)/Phi(ion)) in the CH4 plasma was an important factor for the carbon film formation, and when this ratio reduced to a certain critical value with increasing elapsed deposition time, the deposited film was then re-etched predominately by the secondary higher hydrocarbon ions. At 1.0 Torr where a polymer-like soft carbon film was deposited, such re-etching of the deposited film was not observed.