A method by which a first device (100) performs sidelink transmission and an apparatus for supporting same are presented. The method comprises the steps of: receiving information about a first resource pool set on the basis of a first slot format; reserving a first resource for the sidelink transmission on the basis of the information about the first resource pool; receiving information about a second resource pool set on the basis of a second slot format, after reserving the first resource; and performing the sidelink transmission on the basis of the information about the second resource pool.