A reclining structure of a vehicular seat is provided with: a coupling shaft configured to couple a seat back to a vehicle main body; a slide rail provided at a side part of the vehicle main body and having a curved guide shape; a slider mounted to the slide rail; an attaching and detaching mechanism configured to detachably engage the slider and the seat back with each other; and a slide lock mechanism configured to lock movement of the slider. The slide lock mechanism is provided with: a lock member guided by and mounted to the slider to be slidable in a diametrical direction; a cam member mounted to the slider to straightly push out the lock member in the diametrical direction; and a lock teeth having a teeth face arranged to face in the diametrical direction along the guide shape of the slide rail.