A thermooptic type variable optical attenuator applicable to an array type variable optical attenuator that realizes a low cross talk between adjacent waveguide arrays. The thermooptic type variable optical attenuator (100), using an optical material having a negative thermooptic effect, comprises a multi-mode optical propagation unit (3) provided between single-mode optical waveguides (1, 8) via tapers (2, 7), a heating thin-film heater (4) provided above the multi-mode optical propagation unit (3) so as to be inclined an angle beta to the optical propagation direction of a first optical waveguide (50), and a second optical waveguide (9) optically coupled with the side surface (3S1) of the multi-mode optical propagation unit (3) and inclined an angle 2beta to the optical propagation direction of the first optical waveguide (50). |