To provide a polyolefin-based resin film which shows a low heat seal initiation temperature, can keep a weak heat seal strength by gradually raising the heat seal strength according to an increase in heat sealing temperature in the low-temperature area, causes no welding of the film on a heating surface of a seal bar due to melting of the outer layer of the film during conducting heat seal with the heat seal bar, and shows an excellent heat sealing performance.

The laminate film has two or more layers of the polyolefin-based resins having at least an inner layer and an outer layer. When the inner layers of the laminate films are heat-sealed to each other at 80°C, the heat seal strength is not less than 0.3N/70mm. When the inner layers of the laminate films are heat-sealed to each other at 90°C, the heat seal strength is 0.3 to 3.0N/70mm. When the outer layers of the laminate films are heat-sealed to each other at 90°C, the heat seal strength is not more than 0.1N/70mm.