Yokozawa Shogen (Japanese: 横沢将監) was born in the middle of the 16th century in a samurai family, in the domain of Sendai, Japan. He served the Daimyo of Sendai Date Masamune.

In September 1616, under an order by Date Msamune, Yokozawa went to Mexico on the San Juan Bautista in order to fetch his compatriot Hasekura Rokuemon who was coming back from an embassy to Europe.

His trip proved difficult, and around 100 men on the ship died en route. He arrived in Acapulco in May 1617. He remitted a letter and some merchandise from Date Masamune, and was baptized, receiving the name of Don Alonzo Hacaldo.

The ship sailed on April 1618 for a fourth trans-Pacific travel, and arrived in the Philippines, where she was bought by the local Spanish government in order to "reinforce defenses against Holland forces by all means possible". Luis Sotelo chose to remain in the Philippines due to the worsening anti-Christian situation in Japan, but Yokozawa Shogen managed to leave for Japan together with Hasekura Rokuemon on a trade ship in August 1620.

After his arrival in Japan, Yokozawa is recorded to have renounced the Christian faith and burnt all his Christian-related belongings. Neither the later life of Yokozawa, or his grave are known.