In this paper, a novel 7-DOF haptic device wearable on a human arm is proposed. Different from the conventional haptic devices which employ only mechanical components, the proposed wearable haptic device is formed by both mechanical links/joints and human bones/joints. As a result, such a biomechanical design allows the device to always adapt to human arm's anatomical structure rather than having the operator to adapt to the device's configurations. Considering the anatomical structure of a human arm, the 7-DOF wearable haptic device consists of three sequentially connected modules, i.e., the 3-DOF wrist module, the 1-DOF elbow module, and the 3-DOF shoulder module, which are designed to adapt to the motions of the human arm's skeletal joints at the wrist, elbow, and shoulder respectively. Because of the modular design, these three functional modules can also be dismantled separately for single joint operations. Moreover, this wearable haptic device has three operating modes: passive, resistive, and active modes for various applications, e.g., tele-operation, virtual reality, and rehabilitation.