The present invention provides a storage device and a writing unit diagnosing method, which can determine a defect in a writing unit at an early stage. There is provided a storage device, which includes writing units that write data to a storage medium, current application units that apply a current to the writing units, electric property measurement units that measure the electric property of the writing units at the time of applying a current by the current application units, and obtain electric property measured values, a storage unit that stores the electric property measured values obtained by the electric property measurement units, and a judgment unit that judges whether or not the writing units are abnormal based on the electric property measured values stored in the storage unit.