This work reports our experiments on organizing evaluation tasks aiming at spoken document retrieval (SDR). The NTCIR Project is a series of evaluation workshops designed to enhance research in information access technologies by providing reusable test collections and a forum for researchers. The author's group has proposed the evaluation tasks for SDR at the NTCIR from 2010. They resulted in holding the four successive evaluation tasks called SpokenDoc-1 and 2, and SpokenQuery&Doc-1 and 2. In the SpokenDoc tasks conducted from 2010 to 2013, we designed and evaluated the SDR tasks targeting spontaneously spoken speech. Based on this data collection, we conducted two subtasks: the spoken term detection subtask and the spoken content retrieval subtask. After two rounds of them, we enhanced our research focus with the query part of information retrieval. In the SpokenQuery&Doc tasks conducted from 2013 to 2016, we investigated the information retrieval systems that take advantage of a spontaneously spoken qu...