A pair of lift arms of a skid steer loader, having a simple structure. Each of the pair of right and left lift arms is composed of a first arm and a second arm. The first arm is long in length and constructed from a sheet metal part etc., and the forward end of the first arm is rotatably fitted to a support section vertically upstanding at the rear of a loader body. In the second arm, a connection section, an attachment mounting section, a lateral load receiving section, an actuator mounting section, etc. are formed integrally of cast steel. Inside the second arm is formed a hollow section running from the generally intermediate portion to the forward end of the second arm. Since the second arms located at the forward ends of the lift arms are each integrally formed of the cast steel, the number of parts can be reduced and the production efficiency can be increased. Consequently, the manufacturing cost can be reduced.