A resin pelletizer apparatus (100) is provided with: a die (6) that has a die surface (61) having a die hole (63) formed therein; a rotary blade (21) that cuts a resin extruded from the die hole (63) into a pellet shape in water when being rotated on the die surface (61) in the water; a sensor (150) that detects elastic waves generated by the rotary blade (21) during the rotation on the die surface (61); and a determination unit (121) that monitors the output value of the sensor (150) and determines that an abnormality has occurred when the output value of the sensor (150) is outside a predetermined range (R).