Biguan (pinyin: bǐ guǎn), also known as Le Gong, is a single-reed gas-sounding instrument of the Buyi nationality.

The pen tube is named for its slender shape and is similar to the tube of a writing brush. It is composed of a tube body and a resonance tube, with a total length of 75 cm. The tube body is made of bamboo, and it is mostly made of locally produced water bamboo or fire tube bamboo (also known as pen tube bamboo) with thin tubes, long sections and thin walls. The diameter is 1.5 cm, the inner diameter is 1.1 cm, the head of the tube is closed with a bamboo joint, the middle is transparent, and the tail of the tube is open.

During the Spring Festival, outing in March or half of July, it is the season for the Bouyei people to sing pen songs. In the Bouyei villages on both sides of the Zhangjiang River in Libo County, southern Guizhou, you can often hear the boys blowing and humming. The pen tube, accompanied by the melodious folk songs of the girls, expressed their incomparable joy.