The 4 slot array antenna for 700GHz far-infrared radiation are fabricated on the fused quartz substrates, making use of the dimensions obtained from the model experiments in the microwave region, and the power gain and directivity are obtained experimentally. The properties of fabricated array antenna agree with the theoiy, and 4 slot array antenna on the substrate of which thickness is odd multiples of a quarter dielectric wavelength improve the power gain by 5dB compared with the single slot antenna on both sides ofair and dielectric. These experimental data indicate that the fabricated antennas show the antenna pattern expected from the theory and work as array antennas for 700GHz far-infrared laser radiation.