Abstract: Tube slotting machine for cutting series of transverse slotted openings in flexible corrugated tubing comprises main framework with tube supporting and conveying structure connected thereto for guiding tubing through machine. Cutting structure is adapted to engage tubing as it travels through machine and to cut transverse slotted openings therein. Cutting structure includes plurality of primary cutter blades, and equal number of spaced apart secondary blade pairs are arranged with one primary blade located between each pair. Each secondary blade has curved portion that complements curvature of tubing. Secondary blades are positioned next to exterior of tubing as it moves through machine along its path of travel, and primary cutter blade is shifted across its associated secondary blade pair so that primary blade penetrates tubing and sweeps across secondary blade pair to thereby cut slivered portion from tubing to provide transverse slotted opening therein.