held by the spring retainer 28 fixed to the shaft 24 therefore when the spring 27 is deformed upon rotation of the shaft 24 a restoration force is accumulated in the spring therefore when the latch 17 and the notch 18 are engaged with each other fig1 the latch 17 is pressed to release engagement with the notch 18 therefore the spring 27 of the hop up device 22 hops up the display panel 15 about the hinge 19 by the accumulated energy as shown in fig4 a device 30 for detecting an opening closing state of the display panel 15 is arranged in the main body 12 in this embodiment the device comprises a photosensor unit 30 the photosensor unit 30 is operated by a cam 29 fixed to an outer end portion of the shaft 24 of the hop up device 22 i e opposite end portion of the projection 25 in this embodiment the photosensor unit 30 comprises a housing 31 fixed to the top cover 12a a u shaped photointerrupter 32 housed in the housing a printed circuit board 33 for fixing the photointerrupter i o terminals 34 for the photointerrupter fixed to the printed circuit board and a light shielding segment 35 which can be inserted between the two leg portions of the u shaped portion of the photointerrupter by the cam 29 this photointerrupter 32 is a conventional one and has a laser emitting means provided to one leg portion of the u shaped portion and a light.