During the postoperative hand rehabilitation period, it is recommended that the repaired flexor tendons be continuously glided with sufficient tendon excursion and carefully managed protection to prevent adhesion with adjacent tissues. Thus, finger joints should be passively mobilized through a wide range of motion (ROM) with physiotherapy. During passive mobilization, sequential flexion of the metacarpophalangeal (MCP) joint followed by the proximal interphalangeal (PIP) joint is recommended for maximizing tendon excursion. This paper presents a lightweight device for postoperative flexor tendon rehabilitation that uses a single motor to achieve sequential joint flexion movement. The device consists of an orthosis, a cable, and a single motor. The degree of spatial stiffness and cable path of the orthosis were designed to apply a flexion moment to the MCP joint prior to the PIP joint. The device was tested on both healthy individuals and a patient who had undergone flexor tendon repair surgery, and both flexion and extension movement could be achieved with a wide ROM and sequential joint flexion movement using a single motor.