A laser recorder applicable to computer output microfilm recording apparatus comprises: a housing, a film feed unit having a film cassette loaded with a rolled heat development film; a film take-up unit for taking up the heat development film on a reel or on a tray, including a film storing mechanism for storing cut films sequentially; a main driving unit for driving the heat development film for advancing at a fixed speed for auxiliary scanning for recording image information on the heat development film, including a slackened film relief mechanism for eliminating slackened film around the main driving unit and a stepping motor driving current control circuit for driving the main driving unit at a low and fixed speed; loop detectors for preventing film feed force and film delivery force from working on the main driving unit, an image information recording unit for main scanning, having a laser optical system for scanning the heat development film across the width thereof to record image information recorded on the heat development film thereon; and a heat-development unit for heat-developing the image information recorded on the heat development film, including a delivery driving roller unit and a guide roller unit driven at different speeds respectively for eliminating blackened film around the heat-development unit as well as controlling the heat-development time, a temperature controller for controlling heat-development unit temperature, and a swing roller for separating the film from the heat-development unit when heat-development is not required.