To produce a highly oriented undrawn yarn, having biodegradability, capable of providing a spun yarn excellent in cooling properties and mechanical properties, and further having thermobonding properties.

This biodegradable highly oriented undrawn yarn 1 having a hollow cross section or the highly oriented undrawn yarn having many-leaf- shaped cross section is obtained by a high speed melt-spinning of a thermoplastic aliphatic polyester having a melt flow rate value satisfying the formula 20≤ melt flow rate value (g/10 min) $70 [based on the method described in ASTM D1238(E)] and biodegradability through a spinning cap for the hollow cross section or the many-leaf-shaped cross section at a spinning temperature and spinning velocity of the formulas Tm+40≤ spinning temperature (°C) ≤ Tm+150 (Tm is a melting point), and 2500 < spinning velocity (m/min) ≤ 8000.