This paper addresses a supervisory control problem for time invariant hybrid dynamical systems based on the l-complete approximation scheme by Moor and Raisch ("Discrete supervisory control of hybrid systems based on l-complete approximations," 2002) and partial observation. An underlying hybrid plant is realized by a hybrid state machine with an infinite state space, and its external behavior is described by discrete input/output signals with finite range, and some output signal is assumed to be unmeasurable. For the strongest l-complete approximation of the plant, which is realized by a finite state machine, we present a method to design a finite state supervisor to achieve a given specification. The supervisor cannot observe the unmeasurable output signal. Finally, we show that the finite state supervisor also meets the specification for the underlying hybrid plant.