In order to utilize higher frequency bands above 6 GHz which is an important technical challenge in fifth generation mobile systems and ultra-high speed WLANs, radio propagation channel properties in large variety of deployment scenarios should be thoroughly investigated. This paper presented measurement results in an atrium entrance hall environment at an millimeter-wave band of 58.5 GHz assuming an indoor hotspot access scenario. In this measurement, the channel transfer functions of a wideband signal with 400 MHz bandwidth were measured by rotating high gain horn antennas with 12 and 30 degree half power beamwidth at 25 receiver positions. From the measured double-directional angular delay power spectrum, the multi-path clusters were roughly identified by local peak detection. This paper presented delay and angle domain intercluster characteristics and identified the propagation mechanism of each cluster comparing with ray tracing simulation. The measurement results revealed that the dominant mechanisms of the multi-path clusters are the first-order specular reflection from environment specific large walls and scattering by columns and square pillars.