axial pin 5b also the guide slot at one circumferential location is composed of two shorter guide slots 2 39 and 2 34 arranged in a direction of the optical axis two slots are not always necessary to be in one row in the form of an arrangement wherein a partition p for reinforcement is disposed between the the guide slots 2 39 and 2 34 as shown in fig4 the aforementioned two sliding pins 5 are distanced in a direction of the optical axis and are respectively in engagement with the guide slots 2 39 and 2 34 one of said sliding pin bodies 5 engaging also with the driving member 7 to serve as the driven pin 6 shown in fig1 to 3 also in this embodiment the operation and effect similar to those in fig1 to 3 may be obtained either or both of the sliding pin body 5 and the guide slot 2 may be formed of a resin material as in the cases of fig1 to 3 in the embodiments shown in fig7 to 9 four guide slots 2 spaced apart at an angle of 90 u00b0 are provided in the guide frame 1 engaged with one of two guide slots 2 spaced apart at an angle of 180 u00b0 is a sliding member 4 39 in the form of a strip or band formed of a resin material mounted on the moving frame 3 by means of two set screws and engaged with the other is a sliding pin body 5 engaged with one of another two guide slots 2 spaced apart at an angle of 180 u00b0 are two sliding pin bodies 5 mounted on.