In order to realize a single-layer corporate-fed slot array, a hollow rectangular coaxial line is adopted as a feeding line. A 2×2-element subarray on a hollow rectangular coaxial line for the corporate-fed array is designed for the 60-GHz band. For the wideband operation, a cavity-backed wide slot is adopted as a radiating element. The 5.7% bandwidth for the reflection less than −20 dB is obtained in the subarray by simulation. The performance of a 16×16-element array is evaluated using the result of the designed subarray.