Generation of cells with a loss-of-function mutation in a gene (knockout cells) 
is a valuable technique for studying the function of a given gene product. 
However, if the product of the target gene is essential for cell viability, 
conditional knockout cell lines must be generated. Recently, as gene editing 
technology using CRISPR/Cas9 has developed, it has become possible to produce 
conditional knockout cell lines using this technique. However, to obtain final 
conditional knockout cell lines, it is necessary to perform several experiments 
with multiple complicated steps. In this paper, we introduce an easy and 
efficient method to generate conditional knockout cell lines based on combining 
auxin-inducible degron (AID) technology with CRISPR/Cas9 gene editing. Our 
method only requires performing a single transfection and is therefore an easy 
and rapid method to obtain a conditional knockout cell line.