The development of the receiver for Band 10 (787-950GHz), the highest frequency band in ALMA, is being carried out in the Advanced Environment Test Building of the National Astronomical Observatory of Japan in Mitaka. As part of the development, the performance of a corrugated horn (device to collect radio waves) is evaluated. The corrugated horn was cut out from an aluminum block using the Japanese state-of-the-art cutting technology. The picture shows a cutting model of the prototype corrugated horn for Band 10, viewed with a stereoscopic microscope. The corrugated horn has 10 grooves in 1 mm, and its cutting accuracy will be checked later. Generally, compared with electroforming, cutting can be finished in a shorter period at less cost. It is unprecedented in the world to make a corrugated horn for high frequency with micro-cutting technology like this.