The obligation to settle the administrative matter in a prompt and detailed manner, while applying the simplest possible procedural measures, has the status of a general principle of the administrative procedure. As a result of the amendment made in 2017, a number of changes motivated by the need to speed up and simplify the administrative procedure were introduced into the Code of Administrative Procedure. The procedural law distinguishes the inactivity of the authority from the unreasonable length of proceedings. The first one takes place when the public administration authority did not settle a matter within the period prescribed by the law. The most important of the procedural guarantees of the principle of prompt proceedings is the right to reminder, which can be used to challenge the inactivity in a course of the proceedings. Exhaustion of the reminder opens the way to the control of the state of inaction by the administrative court. Due to low effectiveness of procedural measures applied to prevent inaction of administrative authorities, in article it is postulated to consider the reasons for inertia of authorities in the administrative proceedings.