The temporal structure, or rhythm, is a crucial factor of the voluntary movements. We can generate a rhythm of movements internally, or synchronize the movements with the rhythm of some external stimuli (e.g., music). In some occasions, such synchronization occurs unintentionally, and the rhythm of movements remains even after the music stopped. In attempt to understand the mechanism of such automatic motor rhythm control, we examined the effects of rhythmic repetition of external cues on the subjects' response in a serial reaction time task. Six healthy participants were asked to respond to visual/auditory stimuli (cues) by pressing a button as quick as possible. The cue was presented 11 times/trial (10 intervals/trial) with varying inter-cue intervals (ICIs). In each block of 16 trials, 3 out of 4 possible ICIs (600, 900, 1200, 1500 ms) were used. The participants were told that the three ICIs were randomly intermingled in each trial. However, in 12 out of 16 trials of each block, the sequence contained a train of 2-4 900-ms ICIs (ICI900s). The effect of repetition of the ICI900 on the reaction time (RT) was examined in different types of blocks. In the '900-shortest' block, the ICI900 was combined with 2 longer ICIs (ICI1200 and ICI1500). In the '900-middle' blocks, the ICI900 was combined with 1 shorter (ICI600) and 1 longer (ICI1200 or 1500) ICIs. In the 900-shortest block, the RT was shortened when the ICI900 was repeated. The median RTs after 1, 2, 3, and 4 repetition of the ICI900 were 200, 187, 183, and 169 ms (p < 0.05, Kruskal Wallis test). Such acceleration of response was not observed in the 900-middle blocks. The RT after longer ICI was also influenced by preceding train of the ICI900. The median RTs after ICI1200 and ICI1500 were 175 and 177 ms following a single ICI900, and 193 and 201 ms after a train of multiple (2-4) ICI900, respectively (p < 0.05, Wilcoxon rank sum test). Such delay of response was not observed in the 900-middle blocks. The present results suggest a possibility that when we repeat simple actions, such as cue-guided button press, the repetition of the shortest interval is automatically detected and the rhythm is used to synchronize the subsequent actions.