© 2019 IEEE. At PKC 2018, Chen et al. proposed SOFIA, the first MQ-based digital signature scheme secure in the quantum random oracle model (QROM). SOFIA is constructed by applying an extended version of the Unruh transform (EUROCRYPT 2015) to the MQ-based 5-pass identification scheme (IDS) proposed by Sakumoto et al. (CRYPTO 2011). In this paper, we propose an MQ-based 3-pass IDS with impersonation probability of 1/2 and apply the original version of the Unruh transform to it to obtain a more efficient MQ-based digital signature scheme secure in the QROM. The signature size with our digital signature scheme decreases by about 30% compared with SOFIA.