The present study describes the physical features and the musical effects of expressive gestures performed by a professional orchestra conductor including a preliminary analysis of interpersonal relationships between a conductor and an orchestral player. I videotaped sequences of orchestra rehearsals by Michiyoshi Inoue (Conductor) and the Tokyo Philharmonic Orchestra and used this data in the following analysis. In Analysis 1, I measured the timings and the degrees of synchronization between the physical directions of a conductor and the bowing actions of a concertmaster (a principal violinist regarded as a leader of orchestra) to show the emergent processes of mutual coordinated timing structures. Results show that the largest time differences between their actions were observed on the first day of rehearsals, but those time lags were gradually reduced as the rehearsals proceeded. The longest time lags on the first day may reflect that the conductor made strong efforts to convey his musical intentions to the orchestra rather than to control the precise and/or mechanical timings for their ensemble. In Analysis 2, I sought to investigate the musical and expressive aspects of conductor's gestures on the first day. Through the detailed comparisons with a classification table of the conventional conductor's gestures compiled by Braem & Bräm (2000), the outward appearances and the musical contents of the conductor's gestures on the first day were coded. The conductor and five of orchestral players were interviewed in order to check the conductor's musical intentions underlying his gestures and the players' interpretations or impressions that were conveyed by that conductor's gestures. Findings reveal that the conductor flexibly produced many gesture variations not only in the physical appearances but also in the musical contents, which were beyond the conventional patterns. In some cases the multiple musical directions were simultaneously embodied in a conductor's single gesture in a specific manner which represented the compositional structures. Discussion of these results suggests that the conductor's gestures can be considered as dynamic activities with flexibility and simultaneous multiplicity in meaning, and that these features in the real conductor's gestures must contribute to organizing interpersonally coordinated relationships with the orchestra.