A substrate treatment apparatus according to the embodiment includes: a nozzle which ejects a treatment liquid onto a treatment target surface of a substrate; a trajectory deflector including a trajectory deflecting surface, which is an annular inclined surface that deflects a traveling direction of the treatment liquid ejected from the nozzle and makes the treatment liquid incident on the treatment target surface, the trajectory deflecting surface having an inclination angle varying in a direction of annular extension of the trajectory deflecting surface; and a position changer which moves an incident position of the treatment liquid on the trajectory deflecting surface in the direction of annular extension of the trajectory deflecting surface.