This study developed a timer for bedsore prevention, which measured the elapsed time from the last body movement. The timer employed capacitively coupled electrodes to detect body movement. A change in the capacity due to body movement converted into a voltage change, which generated pulses to stop, reset and restart a timer. The validity of the developed timer was investigated through an experiment, in which body movement was simulated by hand movement. No error was occurred in 30 trials of the experiment, suggesting its validity.