The classic inerter element that generates an inertia force proportional to its relative acceleration has demonstrated effective vibration suppression. However, this technology, characterized by constant inertance, lacks the capability for adaptive control. This study introduces a yoke-type mechanism designed to implement a nonlinear inerter device with adaptive control potential, referred to as the yoke-type inerter. A mechanical model of the proposed nonlinear inerter is developed to illustrate its nonlinear inertial behavior and variable inertance. A prototype yoke-type inerter is fabricated, and dynamic testing is conducted to validate the mechanical model. Analytical solutions for an isolator equipped with the yoke-type inerter are derived to explore its adaptive control potential. A base-isolated structure incorporating the yoke-type inerter is proposed to enhance performance under multiple earthquake levels. The nonlinear inertial behavior of the yoke-type inerter is demonstrated through the mechanical model. Experimental results closely align with theoretical predictions, confirming the effectiveness of the proposed model. Under frequent earthquakes, the isolation displacement of the base-isolated structure with the yoke-type inerter is nearly equivalent to that of the structure using the linear counterpart. However, a marked improvement in isolation displacement reduction is observed for the structure with the yoke-type inerter under rare earthquakes. Thus, the proposed yoke-type inerter can be considered a viable candidate for nonlinear inertance and has the potential to adaptively enhance the seismic performance of base-isolated structures during multi-level earthquakes.